ip: Make use of the inline function dst_metric_locked()

Signed-off-by: Satoru SATOH <satoru.satoh@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 5e3685c..9084055 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1613,7 +1613,7 @@
 		       sizeof(rt->u.dst.metrics));
 		if (fi->fib_mtu == 0) {
 			rt->u.dst.metrics[RTAX_MTU-1] = rt->u.dst.dev->mtu;
-			if (rt->u.dst.metrics[RTAX_LOCK-1] & (1 << RTAX_MTU) &&
+			if (dst_metric_locked(&rt->u.dst, RTAX_MTU) &&
 			    rt->rt_gateway != rt->rt_dst &&
 			    rt->u.dst.dev->mtu > 576)
 				rt->u.dst.metrics[RTAX_MTU-1] = 576;