gluon-mesh-batman-adv-core: adjust rssid config to renamed WLAN interfaces

This should fix the signal strength indicators on the TP-Link CPE210/510.

package/gluon-mesh-batman-adv-core/files/lib/gluon/upgrade/350-gluon-mesh-batman-adv-core-rssid

+#!/usr/bin/lua
+
+local uci = require('luci.model.uci').cursor()
+
+if uci:get('system', 'rssid_wlan0') then
+  uci:set('system', 'rssid_wlan0', 'dev', 'mesh0')
+
+  uci:save('system')
+  uci:commit('system')
+end