Scale the passed pa_cvolume structure so that the maximum volume
* of all channels selected via cm/mask equals max. This also modifies
* the volume of those channels that are unmasked. The proportions
* between the channel volumes are kept. If cm is NULL this call is
* identical to pa_cvolume_scale(). Returns \a v, or NULL on error.
* \since 0.9.16
Scale the passed pa_cvolume structure so that the maximum volume * of all channels selected via cm/mask equals max. This also modifies * the volume of those channels that are unmasked. The proportions * between the channel volumes are kept. If cm is NULL this call is * identical to pa_cvolume_scale(). Returns \a v, or NULL on error. * \since 0.9.16