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/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 20210d7..d1327e4 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -213,6 +213,15 @@
 	dst_hold(new);
 }
 
+static inline void ip6_rt_put(struct rt6_info *rt)
+{
+	/* dst_release() accepts a NULL parameter.
+	 * We rely on dst being first structure in struct rt6_info
+	 */
+	BUILD_BUG_ON(offsetof(struct rt6_info, dst) != 0);
+	dst_release(&rt->dst);
+}
+
 struct fib6_walker_t {
 	struct list_head lh;
 	struct fib6_node *root, *node;