net: propagate NETIF_F_HIGHDMA to vlans

Automatically allows vlans to get NETIF_F_HIGHDMA if underlying device
supports it.

On 32bit arches (and more precisely if CONFIG_HIGHMEM is enabled), it
can help to reduce cost of illegal_highdma() and __skb_linearize()
calls.

Tested on tg3 , bnx2, bonding, this worked very well.

This is a generalization of a patch provided by Yi Zou & Jeff Kirsher.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5058,10 +5058,11 @@ int register_netdevice(struct net_device *dev)
 	if (dev->features & NETIF_F_SG)
 		dev->features |= NETIF_F_GSO;
 
-	/* Enable GRO for vlans by default if dev->features has GRO also.
-	 * vlan_dev_init() will do the dev->features check.
+	/* Enable GRO and NETIF_F_HIGHDMA for vlans by default,
+	 * vlan_dev_init() will do the dev->features check, so these features
+	 * are enabled only if supported by underlying device.
 	 */
-	dev->vlan_features |= NETIF_F_GRO;
+	dev->vlan_features |= (NETIF_F_GRO | NETIF_F_HIGHDMA);
 
 	ret = call_netdevice_notifiers(NETDEV_POST_INIT, dev);
 	ret = notifier_to_errno(ret);