vlan: Don't propagate flag changes on down interfaces.

When (de)configuring a vlan interface, the IFF_ALLMULTI ans IFF_PROMISC
flags are cleared or set on the underlying interface. So, if these flags
are changed on a vlan interface that is not up, the flags underlying
interface might be set or cleared twice.

Only propagating flag changes when a device is up makes sure this does
not happen. It also makes sure that an underlying device is not set to
promiscuous or allmulti mode for a vlan device that is down.

Signed-off-by: Matthijs Kooijman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/8021q/vlan_dev.c

···
 {
 	struct net_device *real_dev = vlan_dev_info(dev)->real_dev;
 
-	if (change & IFF_ALLMULTI)
-		dev_set_allmulti(real_dev, dev->flags & IFF_ALLMULTI ? 1 : -1);
-	if (change & IFF_PROMISC)
-		dev_set_promiscuity(real_dev, dev->flags & IFF_PROMISC ? 1 : -1);
+	if (dev->flags & IFF_UP) {
+		if (change & IFF_ALLMULTI)
+			dev_set_allmulti(real_dev, dev->flags & IFF_ALLMULTI ? 1 : -1);
+		if (change & IFF_PROMISC)
+			dev_set_promiscuity(real_dev, dev->flags & IFF_PROMISC ? 1 : -1);
+	}
 }
 
 static void vlan_dev_set_rx_mode(struct net_device *vlan_dev)