Add ssl intermediate cert from F5 LTM Web GUI?

Yes, you must first import your intermediate CA cert as a SEPARATE cert, which you have already done based on your screenshot. In order to link it with your main test.miccheung.com ssl cert and key you have to create a ClientSSL profile under Profiles->SSL->Client. It is all pretty easy and straightforward. Please read the F5 documentation - I have already posted a link in one of my posts above.