i40e: Add appropriate error message logged for incorrect duplex setting

Nothing logged in dmesg for attempting to set incorrect duplex.
Add appropriate error message logged for incorrect duplex setting.
Signed-off-by: NAlicja Kowalska <alicjax.kowalska@intel.com>
Signed-off-by: NKamil Maziarz <kamil.maziarz@intel.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: NTony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/i40e/i40e_ethtool.c

@@ -1287,8 +1287,10 @@ static int i40e_set_link_ksettings(struct net_device *netdev,
 	 * trying to set something that we do not support.
 	 */
 	if (memcmp(&copy_ks.base, &safe_ks.base,
-		   sizeof(struct ethtool_link_settings)))
+		   sizeof(struct ethtool_link_settings))) {
+		netdev_err(netdev, "Only speed and autoneg are supported.\n");
 		return -EOPNOTSUPP;
+	}
 
 	while (test_and_set_bit(__I40E_CONFIG_BUSY, pf->state)) {
 		timeout--;