can: tree-wide: advertise software timestamping capabilities

Currently, some CAN drivers support hardware timestamping, some do
not. But userland has no method to query which features are supported
(aside maybe of getting RX messages and observe whether or not
hardware timestamps stay at zero).

The canonical way for a network driver to advertised what kind of
timestamping it supports is to implement ethtool_ops::get_ts_info().

This patch only targets the CAN drivers which *do not* support
hardware timestamping. For each of those CAN drivers, implement the
get_ts_info() using the generic ethtool_op_get_ts_info().

This way, userland can do:

| $ ethtool --show-time-stamping canX

to confirm the device timestamping capacities.

N.B. the drivers which support hardware timestamping will be migrated
in separate patches.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20220727101641.198847-6-mailhol.vincent@wanadoo.fr
[mkl: mscan: add missing mscan_ethtool_ops]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

can: slcan: export slcan_ethtool_ops and remove slcan_set_ethtool_ops()

The function slcan_set_ethtool_ops() does one thing: populate
net_device::ethtool_ops. Instead, it is possible to directly assign
this field and remove one function call and slightly reduce the object
size. To do so, export slcan_ethtool_ops so it becomes visible to
sclan-core.c.

This patch reduces the footprint by 14 bytes:

| $ ./scripts/bloat-o-meter drivers/net/can/slcan/slcan.{old,new}.o
| drivers/net/can/slcan/slcan.o
| add/remove: 0/1 grow/shrink: 1/0 up/down: 15/-29 (-14)
| Function old new delta
| slcan_open 1010 1025 +15
| slcan_set_ethtool_ops 29 - -29
| Total: Before=11115, After=11101, chg -0.13%

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20220727104939.279022-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

can: slcan: add ethtool support to reset adapter errors

This patch adds a private flag to the slcan driver to switch the
"err-rst-on-open" setting on and off.

"err-rst-on-open" on - Reset error states on opening command

"err-rst-on-open" off - Don't reset error states on opening command
(default)

The setting can only be changed if the interface is down:

ip link set dev can0 down
ethtool --set-priv-flags can0 err-rst-on-open {off|on}
ip link set dev can0 up

Link: https://lore.kernel.org/all/20220628163137.413025-11-dario.binacchi@amarulasolutions.com
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>