Do not enforce the rule in MP3Extractor that all audio frames in an mp3 file...

Do not enforce the rule in MP3Extractor that all audio frames in an mp3 file must have the same mode

For some mp3 files, the mode can be changed from one audio frame to another. Without
the capability to switch modes, the decoded audio may have lots of artifacts.

bug - 3253310

Change-Id: Id57bb1f204642d15e38a800c72214f6794cfaa37