Merge branch 'refs/heads/t/opus'

Merge branch 'refs/heads/t/opus'

This series abstracts out the custom header concept of ogg/vorbis
streams and introduces a public API for it. The new API is employed
for ogg/opus streams to guarantee that fixed size audio format headers
are used for streaming.

Cooking for six weeks.

* refs/heads/t/opus:
  opus_afh: Use custom header API to strip comment packet.
  ogg: Abstract out custom header code.
  Prefix public functions of ogg_afh_common.c with "oac".
  afh_recv: Downgrade severity of log message.