igc: enable HW vlan tag insertion/stripping by default

This is enabled by default in other Intel drivers I've checked (e1000, e1000e,
iavf, igb and ice). Fixes an out-of-the-box performance issue when running
OpenWrt on typical mini-PCs with igc-supported Ethernet controllers and 802.1Q
VLAN configurations, as ethtool isn't part of the default packages and sane
defaults are expected.

In my specific case, with an Intel N100-based machine with four I226-V Ethernet
controllers, my upload performance increased from under 30 Mb/s to the expected
~1 Gb/s.

Signed-off-by: Rui Salvaterra <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Reviewed-by: Vitaly Lifshits <[email protected]>
Reviewed-by: Kurt Kanzenbach <[email protected]>
Tested-by: Mor Bar-Gabay <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>

Author: rsalvaterra

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

@@ -7125,6 +7125,9 @@ static int igc_probe(struct pci_dev *pdev,
 	netdev->xdp_features = NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_REDIRECT |
 			       NETDEV_XDP_ACT_XSK_ZEROCOPY;
 
+	/* enable HW vlan tag insertion/stripping by default */
+	netdev->features |= NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_CTAG_RX;
+
 	/* MTU range: 68 - 9216 */
 	netdev->min_mtu = ETH_MIN_MTU;
 	netdev->max_mtu = MAX_STD_JUMBO_FRAME_SIZE;