igb: change how we handle alternate mac addresses

This patch allows us to treat the alternate mac address as though it is the
physical address on the adapter.  This is accomplished by letting the
alt_mac_address function to only fail on an NVM error.  If no errors occur
and the alternate mac address is not present then RAR0 is read as the
default mac address.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/igb/e1000_hw.h b/drivers/net/igb/e1000_hw.h
index 4e7850d..fad7cf5 100644
--- a/drivers/net/igb/e1000_hw.h
+++ b/drivers/net/igb/e1000_hw.h
@@ -54,6 +54,8 @@
 #define E1000_FUNC_0     0
 #define E1000_FUNC_1     1
 
+#define E1000_ALT_MAC_ADDRESS_OFFSET_LAN1   3
+
 enum e1000_mac_type {
 	e1000_undefined = 0,
 	e1000_82575,