docs: ABI: sysfs-class-led-trigger-netdev: Document now hidable link_*

Document now hidable link speed modes for the LED netdev trigger.

Link speed modes are now showed only if the named network device
supports them and are hidden if not.

Signed-off-by: Christian Marangi <[e-mail]>
Reviewed-by: Marek Behún <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

Documentation/ABI/testing/sysfs-class-led-trigger-netdev

···
 		speed of 10MBps of the named network device.
 		Setting this value also immediately changes the LED state.
 
+		Present only if the named network device supports 10Mbps link speed.
+
 What:		/sys/class/leds/<led>/link_100
 Date:		Jun 2023
 KernelVersion:	6.5
···
 		If set to 1, the LED's normal state reflects the link state
 		speed of 100Mbps of the named network device.
 		Setting this value also immediately changes the LED state.
+
+		Present only if the named network device supports 100Mbps link speed.
 
 What:		/sys/class/leds/<led>/link_1000
 Date:		Jun 2023
···
 		speed of 1000Mbps of the named network device.
 		Setting this value also immediately changes the LED state.
 
+		Present only if the named network device supports 1000Mbps link speed.
+
 What:		/sys/class/leds/<led>/link_2500
 Date:		Nov 2023
 KernelVersion:	6.8
···
 		If set to 1, the LED's normal state reflects the link state
 		speed of 2500Mbps of the named network device.
 		Setting this value also immediately changes the LED state.
+
+		Present only if the named network device supports 2500Mbps link speed.
 
 What:		/sys/class/leds/<led>/link_5000
 Date:		Nov 2023
···
 		speed of 5000Mbps of the named network device.
 		Setting this value also immediately changes the LED state.
 
+		Present only if the named network device supports 5000Mbps link speed.
+
 What:		/sys/class/leds/<led>/link_10000
 Date:		Nov 2023
 KernelVersion:	6.8
···
 		If set to 1, the LED's normal state reflects the link state
 		speed of 10000Mbps of the named network device.
 		Setting this value also immediately changes the LED state.
+
+		Present only if the named network device supports 10000Mbps link speed.
 
 What:		/sys/class/leds/<led>/half_duplex
 Date:		Jun 2023