sentinel.sh dependency

Main issue is in nikola crontab. sentinel.sh is sourced there and allowed_to_run called. Yet, config_load and other OpenWrt functions is missing as functions.sh is never sourced.

This proposed fix seems to me a straightforward solution, as you source what's needed to run the functions provided. Maybe there are some consequences I missed, so please double check this.

collect/sentinel/sentinel-firewall/files/functions.sh

-. /lib/functions.sh
+#!/bin/sh
+## sentinel-firewall.sh
+#
+# set of firewall rules handling functions intended to be sourced and reused
+# in sentinel-related scripts
+
+# source OpenWrt functions if not sourced yet
+command -v config_load > /dev/null || . /lib/functions.sh
+
 
 # This function enables given option on firewall zone wan unless it is already set
 # to some value.