hal: Add a2dp state check for device routing

- During a2dp to sco transition multiple session
  open failures are seen due to a2dp start failure

- Check a2dp streaming state with BT lib before
  routing audio on a2dp device.
  If a2dp is not ready for streaming, force drop
  audio packets for a2dp path similar to BT HAL

Change-Id: If9fdd2184943c2e25a091067477cf0bcc5dce278