Add max_connected_audio_devices parameter to A2DP Sink init

This movess us off of a hardcoded value for number of connected devices
and allows Java, through the JNI, to have input on the maximum number of
audio devices it would like to have connected. This moves A2DP Sink in
linne with A2DP Source. It will also enable easily configurable
multi-a2dp sink and avrcp controller experiences.

Tag: #refactor
Bug: 180039146
Test: atest BluetoothInstrumentationTests
Change-Id: I98b7d55d8aa53c07af6451f3d5dca529b96739fc