Add TPROXY support for OpenBSD, FreeBSD, NetBSD

Add TPROXY support for OpenBSD, FreeBSD, NetBSD

This adds support for the PF 'divert-to' target which presents the
client and remote IPs directly to Squid in accept() parameters the
way Linux TPROXY target does.

It also adds support for the SO_BINDANY option on outgoing traffic for
client IP address spoofing which completes the TPROXY behaviour.

To enable these features Squid built with --enable-pf-transparent can
be configured with:
  http_port 1234 tproxy