net offloading: Do not mask out NETIF_F_HW_VLAN_TX for vlan.

In netif_skb_features() we return only the features that are valid for vlans
if we have a vlan packet.  However, we should not mask out NETIF_F_HW_VLAN_TX
since it enables transmission of vlan tags and is obviously valid.
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NJesse Gross <jesse@nicira.com>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2023,13 +2023,13 @@ int netif_skb_features(struct sk_buff *skb)
 		return harmonize_features(skb, protocol, features);
 	}
 
-	features &= skb->dev->vlan_features;
+	features &= (skb->dev->vlan_features | NETIF_F_HW_VLAN_TX);
 
 	if (protocol != htons(ETH_P_8021Q)) {
 		return harmonize_features(skb, protocol, features);
 	} else {
 		features &= NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_FRAGLIST |
-				NETIF_F_GEN_CSUM;
+				NETIF_F_GEN_CSUM | NETIF_F_HW_VLAN_TX;
 		return harmonize_features(skb, protocol, features);
 	}
 }