igb: restore EEPROM values of MDICNFG on reset with 82580

On a reset the MDICNFG.Destination and MDICNFG.COM_MDIO
register fields are not restored to the EEPROM default.
This patch modifies the reset code to read the EEPROM
and restore the default values.

Signed-off-by: Nicholas Nunley <nicholas.d.nunley@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@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_defines.h b/drivers/net/igb/e1000_defines.h
index 1d4767f..bbd2ec3 100644
--- a/drivers/net/igb/e1000_defines.h
+++ b/drivers/net/igb/e1000_defines.h
@@ -570,6 +570,10 @@
 
 #define NVM_82580_LAN_FUNC_OFFSET(a) (a ? (0x40 + (0x40 * a)) : 0)
 
+/* Mask bits for fields in Word 0x24 of the NVM */
+#define NVM_WORD24_COM_MDIO         0x0008 /* MDIO interface shared */
+#define NVM_WORD24_EXT_MDIO         0x0004 /* MDIO accesses routed external */
+
 /* Mask bits for fields in Word 0x0f of the NVM */
 #define NVM_WORD0F_PAUSE_MASK       0x3000
 #define NVM_WORD0F_ASM_DIR          0x2000