base-files: provide option to specify label MAC address in board.d

For many devices, MAC addresses cannot be retrieved via the
device tree alias.

To still provide the label MAC address for those, this implements
a second mechanism that will put the address into uci config.
Note that this stores the actual MAC address, whereas in DTS
we reference the bearing device.

This is based on the work of Rosy Song <rosysong@rosinson.com>

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/base-files/files/lib/functions/system.sh

@@ -19,6 +19,7 @@ get_mac_label() {
 
 	[ -n "$macdevice" ] && macaddr=$(get_mac_binary "$basepath/$macdevice/mac-address" 0 2>/dev/null)
 	[ -n "$macaddr" ] || macaddr=$(get_mac_binary "$basepath/$macdevice/local-mac-address" 0 2>/dev/null)
+	[ -n "$macaddr" ] || macaddr=$(uci -q get system.@system[0].label_macaddr)
 	echo $macaddr
 }