[IPSEC]: Add xfrm_input_state helper

This patch adds the xfrm_input_state helper function which returns the
current xfrm state being processed on the input path given an sk_buff.
This is currently only used by xfrm_input but will be used by ESP upon
asynchronous resumption.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 8b2b1b5..8624cbd 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -109,7 +109,7 @@
 	/* A negative encap_type indicates async resumption. */
 	if (encap_type < 0) {
 		async = 1;
-		x = skb->sp->xvec[skb->sp->len - 1];
+		x = xfrm_input_state(skb);
 		seq = XFRM_SKB_CB(skb)->seq;
 		goto resume;
 	}