netfilter: ipset: Introduce new operation to get both setname and family

ip[6]tables set match and SET target need to know the family of the set
in order to reject adding rules which refer to a set with a non-mathcing
family. Currently such rules are silently accepted and then ignored
instead of generating a clear error message to the user, which is not
helpful.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>