You need to go to the Administration section of the product to configure admin AAA authentication: Administration > Admins & Roles > AAA. You're currently configuring the section for WLAN AAA authentication, not Admin AAA authentication.
Once setup, you'll need a little bit of extra configuration on the server side to map LDAP user roles into SZ user roles. Here's a slightly older (don't worry, it's still relevant) knowledgebase article that explains how it works: https://support.ruckuswireless.com/articles/000003228.
If those steps look too much, in SZ 5.1, we added a new feature to support default user mapping so you can avoid the AAA to SZ role mapping definition attributes on the AAA server side.