ipv6: introduce ip6_rt_put()

As suggested by Eric, we could introduce a helper function
for ipv6 too, to avoid checking if rt is NULL before
dst_release().

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index cb7e2de..09482f7 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -663,8 +663,7 @@
 
 		icmpv6_send(skb2, rel_type, rel_code, rel_info);
 
-		if (rt)
-			dst_release(&rt->dst);
+		ip6_rt_put(rt);
 
 		kfree_skb(skb2);
 	}
@@ -1208,7 +1207,7 @@
 			if (dev->mtu < IPV6_MIN_MTU)
 				dev->mtu = IPV6_MIN_MTU;
 		}
-		dst_release(&rt->dst);
+		ip6_rt_put(rt);
 	}
 }