Fix platform-specific types

[chitoku-k]

This PR fixes hard-coded platform-specific types in rscap to let Rust infer them instead because not all environments use the same underlying types for libc’s primitives:

• c_char is i8 in amd64, but u8 in aarch64:
  • https://github.com/rust-lang/libc/blob/0.2.180/src/primitives.rs#L20-L44
• Ioctl is u64 in gnu, but i32 in musl:
  • gnu: https://github.com/rust-lang/libc/blob/0.2.180/src/unix/linux_like/linux/gnu/mod.rs#L17
  • musl: https://github.com/rust-lang/libc/blob/0.2.180/src/unix/linux_like/linux/musl/mod.rs#L51

$ cross check --target=aarch64-unknown-linux-musl
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'

  stable-x86_64-unknown-linux-gnu unchanged - rustc 1.93.0 (254b59607 2026-01-19)

info: self-update is disabled for this build of rustup
info: any updates to rustup will need to be fetched with your system package manager
    Checking rscap v0.3.1 (/project/rscap)
error[E0308]: mismatched types
    --> rscap/src/linux/l2.rs:621:69
     |
 621 |             let res = unsafe { libc::if_indextoname(iface.index()?, if_name_ptr) };
     |                                --------------------                 ^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
     |                                |
     |                                arguments to this function are incorrect
     |
     = note: expected raw pointer `*mut u8`
                found raw pointer `*mut i8`
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/mod.rs:1199:12
     |
1199 |     pub fn if_indextoname(ifindex: c_uint, ifname: *mut c_char) -> *mut c_char;
     |            ^^^^^^^^^^^^^^

error[E0308]: mismatched types
   --> rscap/src/linux/l2.rs:627:27
    |
627 |                 ifr_name: if_name,
    |                           ^^^^^^^ expected `[u8; 16]`, found `[i8; 16]`
    |
    = note: expected array `[u8; 16]`
               found array `[i8; 16]`

error[E0308]: mismatched types
    --> rscap/src/linux/l2.rs:634:47
     |
 634 |                 unsafe { libc::ioctl(self.fd, libc::SIOCSHWTSTAMP, ptr::addr_of_mut!(ifreq)) };
     |                          -----------          ^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u64`
     |                          |
     |                          arguments to this function are incorrect
     |
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/linux_like/mod.rs:1731:20
     |
1731 |             pub fn ioctl(fd: c_int, request: Ioctl, ...) -> c_int;
     |                    ^^^^^
help: you can convert a `u64` to an `i32` and panic if the converted value doesn't fit
     |
 634 |                 unsafe { libc::ioctl(self.fd, libc::SIOCSHWTSTAMP.try_into().unwrap(), ptr::addr_of_mut!(ifreq)) };
     |                                                                  ++++++++++++++++++++

error[E0308]: mismatched types
    --> rscap/src/linux/l3.rs:260:69
     |
 260 |             let res = unsafe { libc::if_indextoname(iface.index()?, if_name_ptr) };
     |                                --------------------                 ^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
     |                                |
     |                                arguments to this function are incorrect
     |
     = note: expected raw pointer `*mut u8`
                found raw pointer `*mut i8`
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/mod.rs:1199:12
     |
1199 |     pub fn if_indextoname(ifindex: c_uint, ifname: *mut c_char) -> *mut c_char;
     |            ^^^^^^^^^^^^^^

error[E0308]: mismatched types
   --> rscap/src/linux/l3.rs:266:27
    |
266 |                 ifr_name: if_name,
    |                           ^^^^^^^ expected `[u8; 16]`, found `[i8; 16]`
    |
    = note: expected array `[u8; 16]`
               found array `[i8; 16]`

error[E0308]: mismatched types
    --> rscap/src/linux/l3.rs:273:47
     |
 273 |                 unsafe { libc::ioctl(self.fd, libc::SIOCSHWTSTAMP, ptr::addr_of_mut!(ifreq)) };
     |                          -----------          ^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u64`
     |                          |
     |                          arguments to this function are incorrect
     |
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/linux_like/mod.rs:1731:20
     |
1731 |             pub fn ioctl(fd: c_int, request: Ioctl, ...) -> c_int;
     |                    ^^^^^
help: you can convert a `u64` to an `i32` and panic if the converted value doesn't fit
     |
 273 |                 unsafe { libc::ioctl(self.fd, libc::SIOCSHWTSTAMP.try_into().unwrap(), ptr::addr_of_mut!(ifreq)) };
     |                                                                  ++++++++++++++++++++

error[E0308]: mismatched types
    --> rscap/src/lib.rs:185:55
     |
 185 |         match unsafe { libc::if_indextoname(if_index, name.as_mut_ptr() as *mut i8) } {
     |                        --------------------           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
     |                        |
     |                        arguments to this function are incorrect
     |
     = note: expected raw pointer `*mut u8`
                found raw pointer `*mut i8`
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/mod.rs:1199:12
     |
1199 |     pub fn if_indextoname(ifindex: c_uint, ifname: *mut c_char) -> *mut c_char;
     |            ^^^^^^^^^^^^^^

error[E0308]: mismatched types
    --> rscap/src/lib.rs:195:45
     |
 195 |         match unsafe { libc::if_nametoindex(self.name.as_ptr() as *const i8) } {
     |                        -------------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*const u8`, found `*const i8`
     |                        |
     |                        arguments to this function are incorrect
     |
     = note: expected raw pointer `*const u8`
                found raw pointer `*const i8`
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/mod.rs:1198:12
     |
1198 |     pub fn if_nametoindex(ifname: *const c_char) -> c_uint;
     |            ^^^^^^^^^^^^^^

error[E0308]: mismatched types
   --> rscap/src/lib.rs:234:23
    |
234 |             ifr_name: array::from_fn(|i| self.name[i] as i8),
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `[u8; 16]`, found `[i8; _]`
    |
    = note: expected array `[u8; 16]`
               found array `[i8; _]`

error[E0308]: mismatched types
    --> rscap/src/lib.rs:248:37
     |
 248 |         if unsafe { libc::ioctl(fd, libc::SIOCGIFHWADDR, ptr::addr_of_mut!(ifr)) } < 0 {
     |                     -----------     ^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u64`
     |                     |
     |                     arguments to this function are incorrect
     |
note: function defined here
    --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.180/src/unix/linux_like/mod.rs:1731:20
     |
1731 |             pub fn ioctl(fd: c_int, request: Ioctl, ...) -> c_int;
     |                    ^^^^^
help: you can convert a `u64` to an `i32` and panic if the converted value doesn't fit
     |
 248 |         if unsafe { libc::ioctl(fd, libc::SIOCGIFHWADDR.try_into().unwrap(), ptr::addr_of_mut!(ifr)) } < 0 {
     |                                                        ++++++++++++++++++++

error[E0308]: mismatched types
   --> rscap/src/linux/l2.rs:629:32
    |
629 |                     ifru_data: ptr::addr_of_mut!(hwtstamp_config) as *mut i8,
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
    |
    = note: expected raw pointer `*mut u8`
               found raw pointer `*mut i8`

error[E0308]: mismatched types
   --> rscap/src/linux/l3.rs:268:32
    |
268 |                     ifru_data: ptr::addr_of_mut!(hwtstamp_config) as *mut i8,
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
    |
    = note: expected raw pointer `*mut u8`
               found raw pointer `*mut i8`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `rscap` (lib) due to 12 previous errors