[Spice-devel] [sound rework 0/3 - try 3] Hopefully, third time is the charm

[Jeremy White]

This is a resend of the patch series that just isolates the celt logic
to make it easier to disable celt and to add additional codecs.

If this seems reasonable, I will follow it with a rebase of the patches
adding Opus support.

This patch series incorporates the following feedback from Christophe:
  * Do not try to change semantics of snd_set_playback_compression
  * use spice_new0 instead of spice_malloc0

It also includes a bug fix whereby we do not dereference the SndCodec
if we receive a null pointer; this fixes crashes where the client and
server do not match capabilities.

It does not include the following two pieces of feedback from Christophe:

 * Did not adjust celt warning; next patch does that
 * Did not remove the get_playback_compression api

   imho, that should be a separate patch.

Cheers,

Jeremy