AudioSink: Fix for gapless offload playback

Gapless mode is not working for offload playback due to mismatch
in flags of current track and next track to be played.

AUDIO_OUTPUT_FLAG_DIRECT is added in AudioTrack flags for current track
which does not match exactly with requested flags for next track.
Because of this mismatch, reuse of the AudioTrack is not allowed.

To fix this, update audio sink flags with requested flags and use
track flags only to setPlaybackRate if AUDIO_OUTPUT_FLAG_DIRECT flag
is not set

Change-Id: I52761ccd854b66a7bc218e83c9b44598771c46f7