[NETFILTER] bridge: code rearrangement for clarity

Cleanup and rearrangement for better style and clarity:
	Split the function nf_bridge_maybe_copy_header into two pieces
	Move copy portion out of line.
	Use Ethernet header size macros.
	Use header file to handle CONFIG_NETFILTER_BRIDGE differences

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 864fbbc..191b861 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -38,13 +38,10 @@
 	if (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb))
 		kfree_skb(skb);
 	else {
-#ifdef CONFIG_BRIDGE_NETFILTER
 		/* ip_refrag calls ip_fragment, doesn't copy the MAC header. */
 		if (nf_bridge_maybe_copy_header(skb))
 			kfree_skb(skb);
-		else
-#endif
-		{
+		else {
 			skb_push(skb, ETH_HLEN);
 
 			dev_queue_xmit(skb);