[Mellanox] Fix generate_dump sysfs copy to copy only files with permission

[noaOrMlnx]

What I did

Fix generate dump script to only copy valid files:

• If the module is not present, copy only presence files.
  error: ERR kernel: sxd_kernel: [error] show_module_frequency: __sx_core_get_module_frequency failed (-14) for module64
• If frequency_support value is 0, don't copy frequency sysfs
  error: ERR kernel: [ 858.655221] sxd_kernel: [error] __sx_core_get_module_frequency: Frequency read is not supported.

How I did it

check the above files content before copying all

How to verify it

run 'show techsupport' on Nvidia switch and validate output

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)