leds: trigger: Introduce a NETDEV trigger

This commit introduces a NETDEV trigger for named device
activity. Available triggers are link, rx, and tx.

Signed-off-by: Ben Whitten <ben.whitten@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

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

@@ -0,0 +1,45 @@
+What:		/sys/class/leds/<led>/device_name
+Date:		Dec 2017
+KernelVersion:	4.16
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Specifies the network device name to monitor.
+
+What:		/sys/class/leds/<led>/interval
+Date:		Dec 2017
+KernelVersion:	4.16
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Specifies the duration of the LED blink in milliseconds.
+		Defaults to 50 ms.
+
+What:		/sys/class/leds/<led>/link
+Date:		Dec 2017
+KernelVersion:	4.16
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Signal the link state of the named network device.
+		If set to 0 (default), the LED's normal state is off.
+		If set to 1, the LED's normal state reflects the link state
+		of the named network device.
+		Setting this value also immediately changes the LED state.
+
+What:		/sys/class/leds/<led>/tx
+Date:		Dec 2017
+KernelVersion:	4.16
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Signal transmission of data on the named network device.
+		If set to 0 (default), the LED will not blink on transmission.
+		If set to 1, the LED will blink for the milliseconds specified
+		in interval to signal transmission.
+
+What:		/sys/class/leds/<led>/rx
+Date:		Dec 2017
+KernelVersion:	4.16
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Signal reception of data on the named network device.
+		If set to 0 (default), the LED will not blink on reception.
+		If set to 1, the LED will blink for the milliseconds specified
+		in interval to signal reception.