[NET]: Wrap netdevice hardware header creation.

Add inline for common usage of hardware header creation, and
fix bug in IPV6 mcast where the assumption about negative return is
an errno. Negative return from hard_header means not enough space
was available,(ie -N bytes).

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 86d908b..8668ab3 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1438,17 +1438,12 @@
 static inline int mld_dev_queue_xmit2(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
+	unsigned char ha[MAX_ADDR_LEN];
 
-	if (dev->hard_header) {
-		unsigned char ha[MAX_ADDR_LEN];
-		int err;
-
-		ndisc_mc_map(&ipv6_hdr(skb)->daddr, ha, dev, 1);
-		err = dev->hard_header(skb, dev, ETH_P_IPV6, ha, NULL, skb->len);
-		if (err < 0) {
-			kfree_skb(skb);
-			return err;
-		}
+	ndisc_mc_map(&ipv6_hdr(skb)->daddr, ha, dev, 1);
+	if (dev_hard_header(skb, dev, ETH_P_IPV6, ha, NULL, skb->len) < 0) {
+		kfree_skb(skb);
+		return -EINVAL;
 	}
 	return dev_queue_xmit(skb);
 }