Floss: Ensure all APIs are present before registering clients

After aosp/c/2748695, some API interfaces will be present later than
Adapter interface.

This CL makes sure all APIs are present than registering client
callbacks.

Bug: 318050299
Test: mma packages/modules/Bluetooth
Tag: #floss
Flag: EXEMPT floss only changes
Change-Id: Ia5f0fdf82fc53401b0297bacb8a897a380429aa1