[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>

drivers/net/hamradio/bpqether.c

@@ -286,7 +286,7 @@ static int bpq_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	skb->protocol = ax25_type_trans(skb, dev);
 	skb_reset_network_header(skb);
-	dev->hard_header(skb, dev, ETH_P_BPQ, bpq->dest_addr, NULL, 0);
+	dev_hard_header(skb, dev, ETH_P_BPQ, bpq->dest_addr, NULL, 0);
 	bpq->stats.tx_packets++;
 	bpq->stats.tx_bytes+=skb->len;