tunnels: add _rcu annotations

(struct ip6_tnl)->next is rcu protected :
(struct ip_tunnel)->next is rcu protected :
(struct xfrm6_tunnel)->next is rcu protected :

add __rcu annotation and proper rcu primitives.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index f28d7c9..ffcd478 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1272,7 +1272,7 @@
 	int (*handler)(struct sk_buff *skb);
 	int (*err_handler)(struct sk_buff *skb, struct inet6_skb_parm *opt,
 			   u8 type, u8 code, int offset, __be32 info);
-	struct xfrm6_tunnel *next;
+	struct xfrm6_tunnel __rcu *next;
 	int priority;
 };