libstagefright: Adding a work around for SurfaceMediaSource

- Do not stop on first call to onBuffersReleased, which presumably
  will be called when producer calls setBufferCount on BufferQueue.
- Do not flush the buffers when stop is issued via onBuffersReleased
  (producer calls disconnect on BufferQueue), instead flush when reset
  is called.

Change-Id: I91448bc87563f2245ad9c9c7150b82c358bfe9e2
CRs-Fixed: 387181