AudioAudioPolicyFocusListener and ducking enforced by framework

Notify AudioPolicyFocusListener an app received
  AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK even when focus is enforced by
  the framework.

Test: see bug
Bug: 37241497
Change-Id: I569e6611fb398955adbcd5bbfbda9d44db4aa729