Refactored and added more tests.Cleaned up netlink a bi.

I've added more tests. We now have almost 55% coverage, I've reorganized netlink_linux codebase and moved the non-RTNETLINK functions at the bottom. I've also added some comments to some functions.

Docker-DCO-1.1-Signed-off-by: Milos Gajdos <milosgajdos83@gmail.com> (github: milosgajdos83)