leds: trigger: netdev: Display only supported link speed attribute

leds: trigger: netdev: Display only supported link speed attribute

With the addition of more link speed mode to the netdev trigger, it was
pointed out that there may be a problem with bloating the attribute list
with modes that won't ever be supported by the trigger as the attached
device name doesn't support them.

To clear and address this problem, change the logic where these
additional trigger modes are listed.

Since the netdev trigger REQUIRE a device name to be set, attach to the
device name change function additional logic to parse the supported link
speed modes using ethtool APIs and show only the supported link speed
modes attribute.

Link speed attribute are refreshed on device_name set and on
NETDEV_CHANGE events.

This only apply to the link speed modes and every other mode is still
provided by default.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20240111160501.1774-1-ansuelsmth@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>