ipvlan: forbid vlan devices on top of ipvlan

Currently we allow the creation of 8021q devices on top of
ipvlan, but such devices are nonfunctional, as the underlying
ipvlan rx_hanlder hook can't match the relevant traffic.

Be explicit and forbid the creation of such nonfunctional devices.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan_main.c

@@ -178,7 +178,7 @@ static int ipvlan_init(struct net_device *dev)
 	dev->state = (dev->state & ~IPVLAN_STATE_MASK) |
 		     (phy_dev->state & IPVLAN_STATE_MASK);
 	dev->features = phy_dev->features & IPVLAN_FEATURES;
-	dev->features |= NETIF_F_LLTX;
+	dev->features |= NETIF_F_LLTX | NETIF_F_VLAN_CHALLENGED;
 	dev->gso_max_size = phy_dev->gso_max_size;
 	dev->gso_max_segs = phy_dev->gso_max_segs;
 	dev->hard_header_len = phy_dev->hard_header_len;