ramips: add label-mac for TL-MR3020 v3

The TP-Link TL-MR3020 v3 only has a single MAC address assigned for
ethernet LAN as well as WiFi. This MAC address is also printed on the
casing.

Signed-off-by: David Bauer <[email protected]>

target/linux/ramips/dts/mt7628an_tplink_tl-mr3020-v3.dts

@@ -12,6 +12,7 @@
 		led-failsafe = &led_power;
 		led-running = &led_power;
 		led-upgrade = &led_power;
+		label-mac-device = &ethernet;
 	};
 
 	chosen {