bluetooth: 6lowpan dev_close never returns error

The function dev_close in current kernel will never return an
error. Later changes will make it void.
Signed-off-by: NStephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bluetooth/6lowpan.c

@@ -618,12 +618,8 @@ static void ifup(struct net_device *netdev)
 
 static void ifdown(struct net_device *netdev)
 {
-	int err;
-
 	rtnl_lock();
-	err = dev_close(netdev);
-	if (err < 0)
-		BT_INFO("iface %s cannot be closed (%d)", netdev->name, err);
+	dev_close(netdev);
 	rtnl_unlock();
 }