[VLAN]: Don't synchronize addresses while the vlan device is down

While the VLAN device is down, the unicast addresses are not configured
on the underlying device, so we shouldn't attempt to sync them.

Noticed by Dmitry Butskoy <buc@odusz.so-cdu.ru>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan.c

@@ -636,6 +636,10 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
 			if (!vlandev)
 				continue;
 
+			flgs = vlandev->flags;
+			if (!(flgs & IFF_UP))
+				continue;
+
 			vlan_sync_address(dev, vlandev);
 		}
 		break;