Add a workaround for the issue in binder RPC session setup

Binder RPC on_connect path doesn't return until the next message for the
session setup comes in. This is a blocker to call on_connect and
on_message separately from Trusty clients.

Test: aosp/3506455
Bug: 382291660
Change-Id: I5b40c27353ce201f0cbe0d9426a4a3f9a784b531