ipv6: ip6_ptr rcu annotations

(struct net_device)->ip6_ptr 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/net/core/dev.c b/net/core/dev.c
index 2c7da3a..365f7f5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5416,7 +5416,7 @@
 		/* paranoia */
 		BUG_ON(netdev_refcnt_read(dev));
 		WARN_ON(rcu_dereference_raw(dev->ip_ptr));
-		WARN_ON(dev->ip6_ptr);
+		WARN_ON(rcu_dereference_raw(dev->ip6_ptr));
 		WARN_ON(dev->dn_ptr);
 
 		if (dev->destructor)