netfilter: ipset: hash:net,iface type introduced

The hash:net,iface type makes possible to store network address and
interface name pairs in a set. It's mostly suitable for egress
and ingress filtering. Examples:

        # ipset create test hash:net,iface
        # ipset add test 192.168.0.0/16,eth0
        # ipset add test 192.168.0.0/24,eth1

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>