Ignore chunk size of SPA_DATA_DmaBuf
dmabufs have no well defined size, so what most producers provide are some nonsensical values. Ideally, it should be zero.
This change makes kpipewire ignore the chunk size if the specified buffer has dmabuf type. memfd and memptr code paths still check the chunk size out of an abundance of caution.
dmabuf buffers that contain no data are expected to have CORRUPTED flag.