mpls: defer ttl decrement in mpls_forward()

Defer ttl decrement to optimize in tx_err case. There is no need
to decrease ttl in the case of goto tx_err.

Signed-off-by: Kangmin Park <l4stpr0gr4m@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mpls/af_mpls.c

@@ -407,7 +407,6 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
 	/* Verify ttl is valid */
 	if (dec.ttl <= 1)
 		goto err;
-	dec.ttl -= 1;
 
 	/* Find the output device */
 	out_dev = rcu_dereference(nh->nh_dev);
@@ -431,6 +430,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
 	skb->dev = out_dev;
 	skb->protocol = htons(ETH_P_MPLS_UC);
 
+	dec.ttl -= 1;
 	if (unlikely(!new_header_size && dec.bos)) {
 		/* Penultimate hop popping */
 		if (!mpls_egress(dev_net(out_dev), rt, skb, dec))