Initial support for FreeBSD platform:
- ether_addr structures has been replaced by MacAddress class,
where applicable;
- ETH_ALEN has been replaced with ETHER_ADDR_LEN

Change-Id: If91e5f0ed325f28ee3189e873c31766444c7c7d0
Authors: Grzegorz Bernacki, Michał Dubiel, Dominik Ermel