From: Myk Taylor <myk@ucla.edu>

IPPROTO_PFSYNC -> 240
INADDR_PFSYNC_GROUP -> 224.0.0.240
ok deraadt@

ok deraadt@

Allows multiple hosts to share an IP address, providing high availability
and load balancing.
Based on code by mickey@, with additional help from markus@
and Marco_Pfatschbacher@genua.de
ok deraadt@

icmp protocol naming particularly with pfctl, since the manpage is
icmp6(4) (not ipv6-icmp(4)).
suggested by espie@, cleared with deraadt@, ok dhartmei@