[IPV6]: Revert recent change to rt6_check_dev().

This reverts a0d78ebf

It causes pings to link-local addresses to fail.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -311,21 +311,12 @@ static inline void rt6_probe(struct rt6_info *rt)
 static inline int rt6_check_dev(struct rt6_info *rt, int oif)
 {
 	struct net_device *dev = rt->rt6i_dev;
-	int ret = 0;
-
-	if (!oif)
-		return 2;
-	if (dev->flags & IFF_LOOPBACK) {
-		if (!WARN_ON(rt->rt6i_idev == NULL) &&
-		    rt->rt6i_idev->dev->ifindex == oif)
-			ret = 1;
-		else
-			return 0;
-	}
-	if (dev->ifindex == oif)
+	if (!oif || dev->ifindex == oif)
 		return 2;
-
-	return ret;
+	if ((dev->flags & IFF_LOOPBACK) &&
+	    rt->rt6i_idev && rt->rt6i_idev->dev->ifindex == oif)
+		return 1;
+	return 0;
 }
 
 static inline int rt6_check_neigh(struct rt6_info *rt)