fix delay when shutting down wifi display

RepeaterSource needs to stop SurfaceMediaSource before stopping
its looper, otherwise the stop could get queued behind the last
read(), which will not return until a new frame comes.

Change SurfaceMediaSource stop to signal frame avalable first, so
that its read() returns EOS to reader upon stop.

Bug: 11677087
Change-Id: Ie331cc8c7f4824fd3930f3e909b53db4463902fb