tunnels: missing rcu_assign_pointer()

xfrm4_tunnel_register() & xfrm6_tunnel_register() should
use rcu_assign_pointer() to make sure previous writes
(to handler->next) are committed to memory before chain
insertion.

deregister functions dont need a particular barrier.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/tunnel6.c b/net/ipv6/tunnel6.c
index 3177fe0..d986472 100644
--- a/net/ipv6/tunnel6.c
+++ b/net/ipv6/tunnel6.c
@@ -51,7 +51,7 @@
 	}
 
 	handler->next = *pprev;
-	*pprev = handler;
+	rcu_assign_pointer(*pprev, handler);
 
 	ret = 0;