libmedia: fix for underrun and gapless issue.

 -change offload shared buffer size to avoid failure to
  restart on an underrun.
 (Merged changeid I4dd9e5e5a7c8aebb34b13f2e6626b73adc2ba557)
 -fix for gap seen during gapless playback due to big
  buffer size.
 (Merged changeid If5234059aa4629e9eb02e236a43214de9ef2204b)

Change-Id: I1ad25d3789aced6b804aa695485341bfa4e97eae