Document newly introduced modes and entry for the LED netdev trigger.

Add documentation for new modes:
- link_10
- link_100
- link_1000
- half_duplex
- full_duplex

Add documentation for new entry:
- hw_control

Also add additional info for the interval entry and the tx/rx modes with
the special case of hw_control ON.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230621092653.23172-1-ansuelsmth@gmail.com


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