can: af_can.c use rcu_barrier() on module unload.

This module uses rcu_call() thus it should use rcu_barrier()
on module unload.
Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Acked-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/can/af_can.c

@@ -903,6 +903,8 @@ static __exit void can_exit(void)
 	}
 	spin_unlock(&can_rcvlists_lock);
 
+	rcu_barrier(); /* Wait for completion of call_rcu()'s */
+
 	kmem_cache_destroy(rcv_cache);
 }