[NET]: Move hardware header operations out of netdevice.

Since hardware header operations are part of the protocol class
not the device instance, make them into a separate object and
save memory.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index ffa9f1c..f151900 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -684,7 +684,7 @@
 		goto tx_error;
 	}
 
-	if (dev->hard_header) {
+	if (dev->header_ops) {
 		gre_hlen = 0;
 		tiph = (struct iphdr*)skb->data;
 	} else {
@@ -1063,8 +1063,9 @@
 
  */
 
-static int ipgre_header(struct sk_buff *skb, struct net_device *dev, unsigned short type,
-			void *daddr, void *saddr, unsigned len)
+static int ipgre_header(struct sk_buff *skb, struct net_device *dev,
+			unsigned short type,
+			const void *daddr, const void *saddr, unsigned len)
 {
 	struct ip_tunnel *t = netdev_priv(dev);
 	struct iphdr *iph = (struct iphdr *)skb_push(skb, t->hlen);
@@ -1091,6 +1092,10 @@
 	return -t->hlen;
 }
 
+static const struct header_ops ipgre_header_ops = {
+	.create	= ipgre_header,
+};
+
 static int ipgre_open(struct net_device *dev)
 {
 	struct ip_tunnel *t = netdev_priv(dev);
@@ -1187,7 +1192,7 @@
 			if (!iph->saddr)
 				return -EINVAL;
 			dev->flags = IFF_BROADCAST;
-			dev->hard_header = ipgre_header;
+			dev->header_ops = &ipgre_header_ops;
 			dev->open = ipgre_open;
 			dev->stop = ipgre_close;
 		}