Remove the SPA_AUDIO_MAX_POSITION define and use the
SPA_AUDIO_MAX_CHANNELS again.
Make a compile time define to override the default max channels of 64.
Make sure we compile the SPA library with the default 64 channels. If
you use the SPA library on a spa_audio_info you will get 64 channel
support, like before. If you want more channels, you will need to make
a padded structure or redefine the MAX_CHANNELS before you use the
spa_audio_info structures. You can use the padded structure with the
new functions that take the structure size.
With the extra checks in the parsing code, we avoid making a
valid spa_audio_info with too many channels that don't fit in the
structure. This means that code that receives a spa_audio_info can
assume there is enough padding for all the channels.
Make a new body.h file with some functions to deal with pod and their
body. Make the iter.h functions use mostly this.
Rework the parser so that it only uses body.h functions. With the separation
of pod+body, we can read and verify the pod once and then use the
verified copy to handle the rest of the body safely.
We do this because iter.h only works in pods in memory that doesn't change
because it is vulnerable to modifications of the data after verifying it.
The new parser is not vulnerable to this and will not cause invalid
memory access when used on shared memory. There is however no need for
atomic operations to read the headers, whever is read is either valid
and useable of invalid and rejected.
See #4822
