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/anycast.c b/net/ipv6/anycast.c
index cdf02be..4963c76 100644
--- a/net/ipv6/anycast.c
+++ b/net/ipv6/anycast.c
@@ -84,7 +84,7 @@
 		rt = rt6_lookup(net, addr, NULL, 0, 0);
 		if (rt) {
 			dev = rt->dst.dev;
-			dst_release(&rt->dst);
+			ip6_rt_put(rt);
 		} else if (ishost) {
 			err = -EADDRNOTAVAIL;
 			goto error;