[NET]: Slightly optimize ethernet address comparison.

We know the thing is at least 2-byte aligned, so take
advantage of that instead of invoking memcmp() which
results in truly horrifically inefficient code because
it can't assume anything about alignment.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethernet/eth.c

@@ -146,6 +146,19 @@ int eth_rebuild_header(struct sk_buff *skb)
 	return 0;
 }
 
+static inline unsigned int compare_eth_addr(const unsigned char *__a, const unsigned char *__b)
+{
+	const unsigned short *dest = (unsigned short *) __a;
+	const unsigned short *devaddr = (unsigned short *) __b;
+	unsigned int res;
+
+	BUILD_BUG_ON(ETH_ALEN != 6);
+	res = ((dest[0] ^ devaddr[0]) |
+	       (dest[1] ^ devaddr[1]) |
+	       (dest[2] ^ devaddr[2])) != 0;
+
+	return res;
+}
 
 /*
  *	Determine the packet's protocol ID. The rule here is that we 
@@ -158,16 +171,15 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	struct ethhdr *eth;
 	unsigned char *rawp;
 
-	skb->mac.raw=skb->data;
+	skb->mac.raw = skb->data;
 	skb_pull(skb,ETH_HLEN);
 	eth = eth_hdr(skb);
 
-	if(*eth->h_dest&1)
-	{
-		if(memcmp(eth->h_dest,dev->broadcast, ETH_ALEN)==0)
-			skb->pkt_type=PACKET_BROADCAST;
+	if (*eth->h_dest&1) {
+		if (!compare_eth_addr(eth->h_dest, dev->broadcast))
+			skb->pkt_type = PACKET_BROADCAST;
 		else
-			skb->pkt_type=PACKET_MULTICAST;
+			skb->pkt_type = PACKET_MULTICAST;
 	}
 
 	/*
@@ -178,10 +190,9 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	 *	seems to set IFF_PROMISC.
 	 */
 
-	else if(1 /*dev->flags&IFF_PROMISC*/)
-	{
-		if(memcmp(eth->h_dest,dev->dev_addr, ETH_ALEN))
-			skb->pkt_type=PACKET_OTHERHOST;
+	else if(1 /*dev->flags&IFF_PROMISC*/) {
+		if (unlikely(!compare_eth_addr(eth->h_dest, dev->dev_addr)))
+			skb->pkt_type = PACKET_OTHERHOST;
 	}
 
 	if (ntohs(eth->h_proto) >= 1536)