netfilter: ipset: bitmap:ip,mac type support

The module implements the bitmap:ip,mac set type in two flavours,
without and with timeout support. In this kind of set one can store
IPv4 address and (source) MAC address pairs. The type supports elements
added without the MAC part filled out: when the first matching from kernel
happens, the MAC part is automatically filled out. The timing out of the
elements stars when an element is complete in the IP,MAC pair.

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