etherdev: Avoid unnecessary byte swap in check for Ethertype

This change takes advantage of the fact that ETH_P_802_3_MIN is aligned to
512 so as a result we can actually ignore the lower 8b when comparing the
Ethertype to ETH_P_802_3_MIN.  This allows us to avoid a byte swap by simply
masking the value and comparing it to the byte swapped value for
ETH_P_802_3_MIN.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethernet/eth.c

@@ -178,7 +178,7 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	if (unlikely(netdev_uses_dsa(dev)))
 		return htons(ETH_P_XDSA);
 
-	if (likely(ntohs(eth->h_proto) >= ETH_P_802_3_MIN))
+	if (likely((eth->h_proto & htons(0xFF00)) >= htons(ETH_P_802_3_MIN)))
 		return eth->h_proto;
 
 	/*