system: users might miss this so put it back

rc.resolv_conf_generate like most rc.* scripting magic should
eventually go way.

src/etc/inc/plugins.inc.d/core.inc

@@ -475,9 +475,10 @@ function core_xmlrpc_sync()
 
 function core_configure()
 {
-    return array(
-        'user_changed' => array('core_user_changed_groups:2'),
-    );
+    return [
+        'dns_reload' => ['system_resolvconf_generate', 'system_hosts_generate'],
+        'user_changed' => ['core_user_changed_groups:2'],
+    ];
 }
 
 /**

src/opnsense/service/conf/actions.d/actions_dns.conf

@@ -1,3 +1,9 @@
+[reload]
+command:/usr/local/sbin/pluginctl -c dns_reload
+parameters:
+type:script_output
+message:rewriting /etc/resolv.conf and /etc/hosts
+
 [query]
 command:/usr/local/opnsense/scripts/dns/query_dns.py
 parameters: --server %s %s