[NETFILTER] ip[6]t_policy: Fix compilation warnings

ip[6]t_policy argument conversion slipped when merging with x_tables

Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>