binder: Use RpcTransport

- after accept() / connect(), call sslAccept() /
  sslConnect(), respectively.
- replace ::send() / ::recv() with RpcTransport::
  send() / recv() / peek() accordingly.

Also refacator binderRpcTest to prepare for TLS implementation.

Test: TH
Test: binderRpcTest
Bug: 190868302

Change-Id: I809345c59a467cd219ebcec7a9db3a3b7776a601