can: etas_es58x: advertise timestamping capabilities and add ioctl support

Currently, userland has no method to query which timestamping features
are supported by the etas_es58x driver (aside maybe of getting RX
messages and observe whether or not hardware timestamps stay at zero).

The canonical way for a network driver to advertise what kind of
timestamping is supports is to implement
ethtool_ops::get_ts_info(). Here, we use the CAN specific
can_ethtool_op_get_ts_info_hwts() function to achieve this.

In addition, the driver currently does not support the hardware
timestamps ioctls. According to [1], SIOCSHWTSTAMP is "must" and
SIOCGHWTSTAMP is "should". This patch fills up that gap by
implementing net_device_ops::ndo_eth_ioctl() using the CAN specific
function can_eth_ioctl_hwts().

[1] kernel doc Timestamping, section 3.1: "Hardware Timestamping
Implementation: Device Drivers"
Link: https://docs.kernel.org/networking/timestamping.html#hardware-timestamping-implementation-device-drivers

Signed-off-by: Vincent Mailhol <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

drivers/net/can/usb/etas_es58x/es58x_core.c

···
  * Copyright (c) 2020, 2021 Vincent Mailhol <[e-mail]>
  */
 
+#include <linux/ethtool.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/usb.h>
···
 static const struct net_device_ops es58x_netdev_ops = {
 	.ndo_open = es58x_open,
 	.ndo_stop = es58x_stop,
-	.ndo_start_xmit = es58x_start_xmit
+	.ndo_start_xmit = es58x_start_xmit,
+	.ndo_eth_ioctl = can_eth_ioctl_hwts,
+};
+
+static const struct ethtool_ops es58x_ethtool_ops = {
+	.get_ts_info = can_ethtool_op_get_ts_info_hwts,
 };
 
 /**
···
 	es58x_init_priv(es58x_dev, es58x_priv(netdev), channel_idx);
 
 	netdev->netdev_ops = &es58x_netdev_ops;
+	netdev->ethtool_ops = &es58x_ethtool_ops;
 	netdev->flags |= IFF_ECHO;	/* We support local echo */
 	netdev->dev_port = channel_idx;