NetUtils: fix PEP8 issues

Having automated flake8 testing it is easier to catch some
issues prior they will cause real bugs; but to be used
with flake8, the code must be PEP8-compliant.

Signed-off-by: Peter V. Saveliev <peter@svinota.eu>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
NetUtils: use IPRoute instead of IPRSocket

Since IPRoute became threadless, it is simpler to use IPRoute
methods like `get_links()` to gather the info.

Signed-off-by: Peter V. Saveliev <peter@svinota.eu>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>