gluon-setup-mode: add fallback led-boot as status

for devices in targets that do no implement `get_status_led` in /etc/diag.sh
and do not have an led-running in their dts

package/gluon-setup-mode/files/lib/gluon/setup-mode/rc.d/S96led

@@ -12,6 +12,9 @@ start() {
 	if [ -z $status_led ]; then
 		status_led="$running"
 	fi
+	if [ -z $status_led ]; then
+		status_led="$boot"
+	fi
 
 	status_led_set_timer 1000 300
 }