igb: clean up code for setting MAC address

BugLink: http://bugs.launchpad.net/bugs/1547674

Drop a bunch of hand written byte swapping code in favor of just doing the
byte swapping ourselves.  The registers are little endian registers storing
a big endian value so if we read the MAC address array as little endian
then we will get the CPU registers into the proper layout.
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from net-next commit c3278587)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -7698,15 +7698,14 @@ static void igb_io_resume(struct pci_dev *pdev)
 static void igb_rar_set_qsel(struct igb_adapter *adapter, u8 *addr, u32 index,
 			     u8 qsel)
 {
-	u32 rar_low, rar_high;
 	struct e1000_hw *hw = &adapter->hw;
+	u32 rar_low, rar_high;
 
 	/* HW expects these in little endian so we reverse the byte order
-	 * from network order (big endian) to little endian
+	 * from network order (big endian) to CPU endian
 	 */
-	rar_low = ((u32) addr[0] | ((u32) addr[1] << 8) |
-		   ((u32) addr[2] << 16) | ((u32) addr[3] << 24));
-	rar_high = ((u32) addr[4] | ((u32) addr[5] << 8));
+	rar_low = le32_to_cpup((__be32 *)(addr));
+	rar_high = le16_to_cpup((__be16 *)(addr + 4));
 
 	/* Indicate to hardware the Address is Valid. */
 	rar_high |= E1000_RAH_AV;