igc: Add ECN support for TSO

Align with other Intel drivers and add ECN support for TSO.

Add NETIF_F_TSO_ECN flag
Signed-off-by: NSasha Neftin <sasha.neftin@intel.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igc/igc_main.c

@@ -4838,6 +4838,7 @@ static int igc_probe(struct pci_dev *pdev,
 	netdev->features |= NETIF_F_SG;
 	netdev->features |= NETIF_F_TSO;
 	netdev->features |= NETIF_F_TSO6;
+	netdev->features |= NETIF_F_TSO_ECN;
 	netdev->features |= NETIF_F_RXCSUM;
 	netdev->features |= NETIF_F_HW_CSUM;
 	netdev->features |= NETIF_F_SCTP_CRC;