Fix VTS PlaybackDataFlowWithTsVideoFilterTest sometimes failed.

[Description]
If filter is started after playback thread, sometimes
filter cannot get data correctly because of timing issue.

Start playback thread after filter is started
so that filter will always get data correctly.

Bug: 235185563
Test:
1. Testcase pass

Change-Id: I97c38dab1ff81c31b4bb48c8015b626b3a6325ed