The lagg(4) interface is based on trunk(4) interface from OpenBSD.
The FreeBSD is the only system that has the FEC protocol, that is a simple alias
to loadbalance protocol and does not implement the ancient Cisco FEC standard.

From now on, we remove the fec protocol from the documentation and keep the FEC
code only for compatibility.

Phabric: D539
Reviewed by: glebius, thompsa
Approved by: glebius
Sponsored by: QNAP Systems Inc.