[NETFILTER]: xt_CONNMARK target, revision 1

Introduces the xt_CONNMARK target revision 1. It uses fixed types, and
also uses the more expressive XOR logic. Futhermore, it allows to
selectively pick bits from both the ctmark and the nfmark in the SAVE
and RESTORE operations.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>