board/aarch64/r2s: control WAN LED with a simple DHCP client monitor

When the interface is up and has a 'proto dhcp' address the WAN LED is
lit up.  When the interface goes down, or loses its DHCP lease, the LED
is turned off.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

board/aarch64/r2s/rootfs/etc/finit.d/wan-monitor.conf

@@ -0,0 +1 @@
+service [12345789] log wan-monitor.sh -- WAN Health monitor

board/aarch64/r2s/rootfs/usr/sbin/wan-monitor.sh

@@ -0,0 +1,41 @@
+#!/bin/sh
+# Background WAN interface monitor.  Lights up WAN LED
+# while the interface has a DHCP address.
+
+LED_FILE="/run/led/wan-up"
+PID_FILE="/run/$(basename "$0").pid"
+
+check_wan()
+{
+    ip_info=$(ip a show wan)
+
+    if echo "$ip_info" | grep -q "inet .* proto dhcp"; then
+        [ ! -f "$LED_FILE" ] && touch "$LED_FILE"
+    else
+        [ -f "$LED_FILE" ] && rm "$LED_FILE"
+    fi
+}
+
+cleanup()
+{
+    rm -f "$LED_FILE"
+    rm -f "$PID_FILE"
+    exit 0
+}
+
+trap 'cleanup' TERM INT HUP QUIT
+echo $$ > "$PID_FILE"
+
+remaining_time=$((1800 - $(awk '{print int($1)}' /proc/uptime)))
+[ "$remaining_time" -lt 0 ] && remaining_time=0
+
+while [ "$remaining_time" -gt 0 ]; do
+    check_wan
+    sleep 1
+    remaining_time=$((remaining_time - 1))
+done
+
+while :; do
+    check_wan
+    sleep 5
+done