IMS : Fix the user handle being passed to Telecom

- Currently during SDK API calls for start conference,
  we are clearing the Binder identity and send the user handle
  to CallsManager, due to which Guest restriction are not
  applied properly.

- To fix this we need to the userhandle before clearing the
  identity and then invoke CallsManager API.

Change-Id: I4f74d46154b41b6e082af0869efdcceaaafb1f7f
Bug: 326376472