libstagefright: use extended extractor for AC3/EAC3 formats

- Use extended extractor to parse Dolby AC3/EAC3 formats.
  Default extractor cannot parse multi-channel AC3/EAC3
  files properly

CRs-Fixed: 646269
Change-Id: Id097533790b69f5a26d5b92fb4fd64d03b622d68