tipc: use RCU to protect media_ptr pointer

Now the media_ptr pointer is protected with tipc_net_lock write lock
on write side; tipc_net_lock read lock is used to read side. As the
part of effort of eliminating tipc_net_lock, we decide to adjust the
locking policy of media_ptr pointer protection: on write side, RTNL
lock is use while on read side RCU read lock is applied.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Tested-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
index 2fa86bd..a983b30 100644
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -128,7 +128,7 @@
  * care of initializing all other fields.
  */
 struct tipc_bearer {
-	void *media_ptr;			/* initalized by media */
+	void __rcu *media_ptr;			/* initalized by media */
 	u32 mtu;				/* initalized by media */
 	struct tipc_media_addr addr;		/* initalized by media */
 	char name[TIPC_MAX_BEARER_NAME];