[NETFILTER]: Prepare {ipt,ip6t}_policy match for x_tables unification

The IPv4 and IPv6 version of the policy match are identical besides address
comparison and the data structure used for userspace communication. Unify
the data structures to break compatiblity now (before it is released), so
we can port it to x_tables in 2.6.17.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>