libstagefright: set frame packing from codec config

- From ACodec call to configure codec is triggered but there is no frame
  packing call
- In default configuration, clips may fail if the proper frame packing
  mode is not set
- Codec config and frame packing are currently done in two separate calls.
  Fix is to trigger frame packing from within the codec config call as
  there is no reason to call each separately

Change-Id: I0455d446cd862b5e7373e3bcb9ad4bfdf7826d18
CRs-Fixed: 648894
libstagefright - Fix seek on audio having empty stss block

Ignore stss block for audio even if its present, all audio
sample are sync samples itself, self decodeable and playable.

Parsing this block for audio restricts audio seek to few entries
available in this block, sometimes 0, which is undesired.

CRs-Fixed: 664870
Change-Id: If3208d5c0557d3eaeddf875d6c6762bd870c439b