How to access catalog item variable and make mandatory on change of malty row variableset ServiceNow

[Nandu4]

I have scenario where if more than 5 ip address are getting added through new request or existing , i need to show message and make addtional comment feild mandatory as mandatory which is in catalog item. So i have write script onchange of ip address which is mrv message is working fine but mandatory is not working 

var partner_id = g_service_catalog.parent.getValue("u_aoi_partner");

    var aoc_ga = new GlideAjax("XXXXXX");

    aoc_ga.addParam("sysparm_name", "getRowCountofipAddress");

    aoc_ga.addParam("partner_info", partner_id);

    aoc_ga.getXMLAnswer(result);

    function result(response) {

        var rowCountofIPAddress = parseInt(response, 10);

        if (rowCountofIPAddress < 5) {

            var mrvs = g_service_catalog.parent.getValue('ip_address_to_be_added');

            if (mrvs.length > 2) {

                var mrvsData = parseInt((JSON.parse(mrvs).length), 10);

                var totalRowCount = mrvsData + rowCountofIPAddress;

                if (totalRowCount == 5) {

                    g_form.setMandatory('u_aoi_additional_information', true);

                    g_form.showFieldMsg("u_aoi_ip_address", "More than 5 IP Addresses have been requested or are already whitelisted for your Company. Please provide a justification of the need in the field below.");

                }

            }

        } else {

           g_form.setMandatory('u_aoi_additional_information', true);

            g_form.showFieldMsg("u_aoi_ip_address", "More than 5 IP Addresses have been requested or are already whitelisted for your Company. Please provide a justification of the need in the field below.");

        }

    }