audiopolicy: optimize voice call start latency

MT call setup latency is more than 500ms because voice call
setup will occur only after the primary output device routing.
Fix by reducing the routing delay. This does not affect the
RINGTONE playback as the reduced delay is enough to complete
RINGTONE playback before voice call device is setup.

Change-Id: I77cb2ddb5a9154ffd2ac1620351992686e580f8a