libbinder: empty ping transaction

It came up recently that the libbinder ping transaction uses 4-bytes in
the reply header, but it really only needs to use the binder return
code (how servicemanager did it before when written in C).

Fixes: 137203409
Test: TH
Change-Id: I4555fdba0f80263caa3f3727ef5c5458d160a585
3 files changed