conntrack: Allow specified alg port numbers.

conntrack: Allow specified alg port numbers.

Algs can use variable control port numbers for servers.
The main use case is a kind of feeble security measure; the
thinking being by some is that it obscures the alg traffic.
It is really not very effective, but the kernel has this
capability. This patch mimics the capability.

Signed-off-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>