xfrm: Use __skb_queue_tail in xfrm_trans_queue

We do not need locking in xfrm_trans_queue because it is designed
to use per-CPU buffers.  However, the original code incorrectly
used skb_queue_tail which takes the lock.  This patch switches
it to __skb_queue_tail instead.
Reported-and-tested-by: Artem Savkov <asavkov@redhat.com>
Fixes: acf568ee ("xfrm: Reinject transport-mode packets...")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_input.c

@@ -518,7 +518,7 @@ int xfrm_trans_queue(struct sk_buff *skb,
 		return -ENOBUFS;
 
 	XFRM_TRANS_SKB_CB(skb)->finish = finish;
-	skb_queue_tail(&trans->queue, skb);
+	__skb_queue_tail(&trans->queue, skb);
 	tasklet_schedule(&trans->tasklet);
 	return 0;
 }