Fix enable/disable behavior and improve effects

- when android requests audioeffect to become disabled, the effect
  must acknowledge its safe removal by returning -ENODATA error code
  from process(). We just return -ENODATA immediately.

- Improve compression to better deal with very sharp level changes.

Change-Id: I8f280f5ae47e9ae4bfad65fcac9b2603eaf7f540