[IPSEC]: Use the correct family for input state lookup

When merging the input paths of IPsec I accidentally left a hard-coded
AF_INET for the state lookup call.  This broke IPv6 obviously.  This
patch fixes by getting the input callers to specify the family through
skb->cb.

Credit goes to Kazunori Miyazawa for diagnosing this and providing an
initial patch.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>