Remove root check at startup

[marek22k]

Background: A process, especially a long-running process that has contact with the outside world, should not have to start with privileged access. With the help of the capabilities system, it is possible to assign individual required permissions to the process and thus also dispense with root privileges (example CapabilityBoundingSet/AmbientCapabilities=CAP_NET_ADMIN CAP_NET_RAW in systemd).

Closes #39, #42

[marek22k]

"It works for me" ... great, thanks for the help. So, I asked because I didn't remember what decision I made in the other projects, and now I've checked myself since you were too lazy to bother, the conclusion is -- all the other projects have the same check. One of the many reasons for this is that all of these multicast routing daemons run on all UNIX systems out there with the MROUTING kernel stack, not just Linux. So I'm going to have to ask you to take that into account when reworking this patch.

As far as I understand the source code, the root check does not request any rights or similar, but simply terminates the program if it is not executed as root. Therefore, any option to execute the program without privileges is removed.
If I run the program on BSD (or another Unix OS) without root privileges, this change means that I no longer receive a error, but instead another error is thrown (for example, on Linux `pim6sd: 19:38:49.173 MLD6 socket: Operation not permitted).

Alternatively, to cover both user-friendliness and my use case, I could keep the root check but only issue a warning (no error that terminates the program). What do you think is better?