i40e: don't advertise IFF_SUPP_NOFCS

[ Upstream commit a24162f ]

i40e advertises IFF_SUPP_NOFCS, allowing users to use the SO_NOFCS
socket option. However, this option is silently ignored, as the driver
does not check skb->no_fcs, and always enables FCS insertion offload.

Fix this by removing the advertisement of IFF_SUPP_NOFCS.

This behavior can be reproduced with a simple AF_PACKET socket:

  import socket
  s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW)
  s.setsockopt(socket.SOL_SOCKET, 43, 1) # SO_NOFCS
  s.bind(("eth0", 0))
  s.send(b'\xff' * 64)

Previously, send() succeeds but the driver ignores SO_NOFCS.
With this change, send() fails with -EPROTONOSUPPORT, as expected.

Fixes: 41c445f ("i40e: main driver core")
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260416-iwl-net-submission-2026-04-14-v2-9-686c33c9828d@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: hyperenju

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -13883,7 +13883,6 @@ static int i40e_config_netdev(struct i40e_vsi *vsi)
 	netdev->neigh_priv_len = sizeof(u32) * 4;
 
 	netdev->priv_flags |= IFF_UNICAST_FLT;
-	netdev->priv_flags |= IFF_SUPP_NOFCS;
 	/* Setup netdev TC information */
 	i40e_vsi_config_netdev_tc(vsi, vsi->tc_config.enabled_tc);