igb: use mac loopback for i354 backplane

We can't know what PHY is to be used for i354 backplane, so use MAC
loopback for ethtool tests.

Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

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

@@ -1665,8 +1665,8 @@ static int igb_setup_loopback_test(struct igb_adapter *adapter)
 		(hw->device_id == E1000_DEV_ID_DH89XXCC_SERDES) ||
 		(hw->device_id == E1000_DEV_ID_DH89XXCC_BACKPLANE) ||
 		(hw->device_id == E1000_DEV_ID_DH89XXCC_SFP) ||
-		(hw->device_id == E1000_DEV_ID_I354_SGMII)) {
-
+		(hw->device_id == E1000_DEV_ID_I354_SGMII) ||
+		(hw->device_id == E1000_DEV_ID_I354_BACKPLANE_2_5GBPS)) {
 			/* Enable DH89xxCC MPHY for near end loopback */
 			reg = rd32(E1000_MPHY_ADDR_CTL);
 			reg = (reg & E1000_MPHY_ADDR_CTL_OFFSET_MASK) |