fix flush on HW A/V sync tracks

Fix mismatch between track flags on client and server side
when HW A/V sync is requested.

The audio track was connected to a direct output by the audio policy
manager but the client failed to set the direct flag when creating
the track resulting in the direct flag not being set in audio flinger.

Bug: 19665934.
Change-Id: I0a5257b20bf76c9c4d89bc2ad9b44777b81f13bf