Rather than listening on two sockets, one for IPv4 and one for IPv6 the
csync server listens on one IPv6 socket and uses IPv4 mapped IPv6 addresses
to support IPv4. This IPv6 feature is disabled by default on FreeBSD so
add a patch to enable it on the server socket.
Tested by: email@example.com
Approved by: firstname.lastname@example.org (maintainer)