[XFRM]: Eliminate refcounting confusion by creating __xfrm_state_put().

We often just do an atomic_dec(&x->refcnt) on an xfrm_state object
because we know there is more than 1 reference remaining and thus
we can elide the heavier xfrm_state_put() call.

Do this behind an inline function called __xfrm_state_put() so that is
more obvious and also to allow us to more cleanly add refcount
debugging later.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/key/af_key.c b/net/key/af_key.c
index ae86d23..b2d4d1d 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -1423,7 +1423,7 @@
 
 	if (err < 0) {
 		x->km.state = XFRM_STATE_DEAD;
-		xfrm_state_put(x);
+		__xfrm_state_put(x);
 		goto out;
 	}