bridge: Use rcu_barrier() instead of syncronize_net() on unload.

When unloading modules that uses call_rcu() callbacks, then we must
use rcu_barrier().  This module uses syncronize_net() which is not
enough to be sure that all callback has been completed.
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NJesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br.c

@@ -93,7 +93,7 @@ static void __exit br_deinit(void)
 
 	unregister_pernet_subsys(&br_net_ops);
 
-	synchronize_net();
+	rcu_barrier(); /* Wait for completion of call_rcu()'s */
 
 	br_netfilter_fini();
 #if defined(CONFIG_ATM_LANE) || defined(CONFIG_ATM_LANE_MODULE)