netfilter: af_info: add network namespace parameter to route hook

This is required to eventually replace the rt6_lookup call in
xt_addrtype.c with nf_afinfo->route().

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Patrick McHardy <kaber@trash.net>