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>
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index b5860b9..24fd613 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -459,6 +459,7 @@
 	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();