Audio policy: fix HwModuleCollection::getDeviceDescriptor

  The deprecated method AudioManager.isBluetoothA2dpOn() calls
getDeviceConnectionState on APM with an empty address, which
caused HwModuleCollection::getDeviceDescriptor to set an empty
address on the DeviceDescriptor for the currently connected
A2DP device. This method is called by MediaRouter.
  When the address was reset, the java listener for audio device
connection monitoring was reporting the connection of an A2DP
device with an empty address, which in turn caused AvrcpManager
to behave as if the audio device connection failed.
  If MediaRouter called isBluetoothA2dpOn() before AvrcpManager
received its called for device connection, the error would occur.

Bug: 132416679
Test: call isBluetoothA2dpOn() and check for valid address in dumpsys media.audio_policy
Test: atest AudioServiceHostTest#testInjectForRecord ; atest AudioHostTest ; atest AudioPlaybackCaptureTest
Change-Id: I1370edbbca46657506a990855d06a176f07c54d3