Initial support for FreeBSD platform:
- ethhdr structures have been replaced with ether_header
- icmphdr structures have been replcaed with icmp
- iphdr structures have been replcaed with ip

All above replacements have been done to make the code common
with the BSD.

Change-Id: I8554ab3017714e30b406dfdd0a40799de9c0a9a4
Authors: Grzegorz Bernacki, Michał Dubiel, Dominik Ermel