AVRCP Controller manage active device

Add function to allow the active A2DP sink's peer to be managed via
JNI.  The new logic only decodes A2DP audio packets from the active
device, rather than any device as long as the active device was in
streaming mode.  With this change an A2DP sink may connect up to
kDefaultMaxConnectedAudioDevices A2DP sources and have media browsing
and playback managed correctly.

Bug: 132642754
Test: change constant, connect two devices and play via browsing.
Change-Id: Ia4633aaf2f092a95bd816cf6ca7101210ebcf222