net: lan743x: implement ndo_hwtstamp_get()

Permit programs such as "hwtstamp_ctl -i eth0" to retrieve the current
timestamping configuration of the NIC, rather than returning "Device
driver does not have support for non-destructive SIOCGHWTSTAMP."

The driver configures all channels with the same timestamping settings.
On TX, retrieve the settings of the first channel, those should be
representative for the entire NIC. On RX, save the filter settings in a
new adapter field.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250514151931.1988047-2-vladimir.oltean@nxp.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>