StagefrightRecorder: Pause audio encoder on recorder pause

  When the recorder is paused, OMXCodec-based audio encoders will wait
  for output buffers, timing out after 3 seconds. Pause the audio encoder
  to avoid a timeout error.

CRs-Fixed: 634301
Change-Id: I99b95bf356f87e9c18c763c542cbfcc13bc54fb1