Retire 4.4BSD raw sockets

Until today the remnants of the original code had provided some aid
in implementation of routing socket and IPSEC key socket. There were
more obfuscation rather than generalisation with this aid.

A historical reference on the original idea of the raw sockets can
be found in chapter 11 of 4.4BSD System Manager Manual:

https://raw.githubusercontent.com/sergev/4.4BSD-Lite2/master/usr/share/doc/smm/18.net.pdf

Reviewed by: melifaro
Differential revision: https://reviews.freebsd.org/D36124