ethtool: RX software timestamp for all

All devices support SOF_TIMESTAMPING_RX_SOFTWARE by virtue of
net_timestamp_check() being called in the device independent code.

Move the responsibility of reporting SOF_TIMESTAMPING_RX_SOFTWARE and
SOF_TIMESTAMPING_SOFTWARE, and setting PHC index to -1 to the core.
Device drivers no longer need to use them.
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Link: https://lore.kernel.org/netdev/661550e348224_23a2b2294f7@willemb.c.googlers.com.notmuch/Co-developed-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240901112803.212753-2-gal@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/common.c

@@ -692,20 +692,21 @@ int __ethtool_get_ts_info(struct net_device *dev, struct kernel_ethtool_ts_info
 {
 	const struct ethtool_ops *ops = dev->ethtool_ops;
 	struct phy_device *phydev = dev->phydev;
+	int err = 0;
 
 	memset(info, 0, sizeof(*info));
 	info->cmd = ETHTOOL_GET_TS_INFO;
+	info->phc_index = -1;
 
 	if (phy_is_default_hwtstamp(phydev) && phy_has_tsinfo(phydev))
-		return phy_ts_info(phydev, info);
-	if (ops->get_ts_info)
-		return ops->get_ts_info(dev, info);
+		err = phy_ts_info(phydev, info);
+	else if (ops->get_ts_info)
+		err = ops->get_ts_info(dev, info);
 
-	info->so_timestamping = SOF_TIMESTAMPING_RX_SOFTWARE |
+	info->so_timestamping |= SOF_TIMESTAMPING_RX_SOFTWARE |
 				 SOF_TIMESTAMPING_SOFTWARE;
-	info->phc_index = -1;
 
-	return 0;
+	return err;
 }
 
 int ethtool_get_phc_vclocks(struct net_device *dev, int **vclock_index)