xen-netfront: Avoid unaligned accesses to IP header

Align ip header to a 16 byte boundary to avoid unaligned
access like other drivers.
Without this patch, xen-netfront doesn't work well on ia64.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/xen-netfront.c

@@ -239,11 +239,14 @@ static void xennet_alloc_rx_buffers(struct net_device *dev)
 	 */
 	batch_target = np->rx_target - (req_prod - np->rx.rsp_cons);
 	for (i = skb_queue_len(&np->rx_batch); i < batch_target; i++) {
-		skb = __netdev_alloc_skb(dev, RX_COPY_THRESHOLD,
+		skb = __netdev_alloc_skb(dev, RX_COPY_THRESHOLD + NET_IP_ALIGN,
 					 GFP_ATOMIC | __GFP_NOWARN);
 		if (unlikely(!skb))
 			goto no_skb;
 
+		/* Align ip header to a 16 bytes boundary */
+		skb_reserve(skb, NET_IP_ALIGN);
+
 		page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
 		if (!page) {
 			kfree_skb(skb);