netfilter: xtables: connlimit revision 1

This adds destination address-based selection. The old "inverse"
member is overloaded (memory-wise) with a new "flags" variable,
similar to how J.Park did it with xt_string rev 1. Since revision 0
userspace only sets flag 0x1, no great changes are made to explicitly
test for different revisions.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>