AAudio: add setBufferCapacity()

This is needed so that an app can request a larger buffer.
Also fix a bug related to passing configuration data to the service.

Test: test_aaudio.cpp
Change-Id: Idd3066c84f6bac76a5d545b12081bc311025a6c3
Signed-off-by: Phil Burk <philburk@google.com>