System: High Availability - when nosync is set on the secondary machine for a vip, the record seems to be added twice as merge_config_attributes() solves this generically for all types. exclude no sync from the $vipbackup in the custom handling code to fix this.

closes https://github.com/opnsense/core/issues/8911

src/etc/inc/xmlrpc/legacy.inc

@@ -184,6 +184,8 @@ function restore_config_section_xmlrpc($new_config)
                 if (!array_key_exists($vipKey, $vhidVipsInNewConfig)) {
                     unset($config['virtualip']['vip'][$vipindex]);
                 }
+            } elseif (!empty($vip['vhid']) && !empty($vip['nosync'])) {
+                null; /* merge_config_attributes() will preserve these records */
             } elseif (!isset($vhidVipsInNewConfig[$vipKey])) {
                 $vipbackup[$vipKey] = $vip;
             }