lapbeth: Release ->ethdev when unregistering device.

Otherwise it leaks forever.

Based upon a report by Roland <devzero@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wan/lapbether.c

@@ -459,6 +459,7 @@ static void __exit lapbeth_cleanup_driver(void)
 	list_for_each_safe(entry, tmp, &lapbeth_devices) {
 		lapbeth = list_entry(entry, struct lapbethdev, node);
 
+		dev_put(lapbeth->ethdev);
 		unregister_netdevice(lapbeth->axdev);
 	}
 	rtnl_unlock();