etherdev: Fix sparse error, make test usable by other functions

This change does two things.  First it fixes a sparse error for the fact
that the __be16 degrades to an integer.  Since that is actually what I am
kind of doing I am simply working around that by forcing both sides of the
comparison to u16.

Also I realized on some compilers I was generating another instruction for
big endian systems such as PowerPC since it was masking the value before
doing the comparison.  So to resolve that I have simply pulled the mask out
and wrapped it in an #ifndef __BIG_ENDIAN.

Lastly I pulled this all out into its own function.  I notices there are
similar checks in a number of other places so this function can be reused
there to help reduce overhead in these paths as well.

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

include/linux/etherdevice.h

@@ -190,6 +190,24 @@ static inline bool is_valid_ether_addr(const u8 *addr)
 	return !is_multicast_ether_addr(addr) && !is_zero_ether_addr(addr);
 }
 
+/**
+ * eth_proto_is_802_3 - Determine if a given Ethertype/length is a protocol
+ * @proto: Ethertype/length value to be tested
+ *
+ * Check that the value from the Ethertype/length field is a valid Ethertype.
+ *
+ * Return true if the valid is an 802.3 supported Ethertype.
+ */
+static inline bool eth_proto_is_802_3(__be16 proto)
+{
+#ifndef __BIG_ENDIAN
+	/* if CPU is little endian mask off bits representing LSB */
+	proto &= htons(0xFF00);
+#endif
+	/* cast both to u16 and compare since LSB can be ignored */
+	return (__force u16)proto >= (__force u16)htons(ETH_P_802_3_MIN);
+}
+
 /**
  * eth_random_addr - Generate software assigned random Ethernet address
  * @addr: Pointer to a six-byte array containing the Ethernet address

net/ethernet/eth.c

@@ -179,7 +179,7 @@ __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((eth->h_proto & htons(0xFF00)) >= htons(ETH_P_802_3_MIN)))
+	if (likely(eth_proto_is_802_3(eth->h_proto)))
 		return eth->h_proto;
 
 	/*