net: use skb_unref() in napi_consume_skb()

The commit 83ada39bb79d ("net: factor out a helper to decrement the
skb refcount") provided and used a helper for decrementing skb usage,
but I missed at least a spot for it.

This change remove some more duplicated code reusing skb_unref() in
napi_consume_skb(), too. The helper uses an additional, unneeded
unlikely(!skb) test - napi_consume_skb() already check it a few lines
above - but the compiler is smart enough to optimize the duplicated
test out.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -817,10 +817,9 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 		return;
 	}
 
-	if (likely(atomic_read(&skb->users) == 1))
-		smp_rmb();
-	else if (likely(!atomic_dec_and_test(&skb->users)))
+	if (!skb_unref(skb))
 		return;
+
 	/* if reaching here SKB is ready to free */
 	trace_consume_skb(skb);