igb: SERDES loopback sigdetect bit on i210 devices

This patch implements SERDES loopback configuration for i210 devices by
unsetting sigdetect bit, so as to fix Ethtool loopback test failure. Old
sigdetect code is also simplified to take care of all devices newer than 82580

Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@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

@@ -1678,17 +1678,12 @@ static int igb_setup_loopback_test(struct igb_adapter *adapter)
 		wr32(E1000_CONNSW, reg);
 
 		/* Unset sigdetect for SERDES loopback on
-		 * 82580 and i350 devices.
+		 * 82580 and newer devices.
 		 */
-		switch (hw->mac.type) {
-		case e1000_82580:
-		case e1000_i350:
+		if (hw->mac.type >= e1000_82580) {
 			reg = rd32(E1000_PCS_CFG0);
 			reg |= E1000_PCS_CFG_IGN_SD;
 			wr32(E1000_PCS_CFG0, reg);
-			break;
-		default:
-			break;
 		}
 
 		/* Set PCS register for forced speed */