When the input buffer contained multiple NAL's the second one would keep the non delta-unit flag for a key frame. The delta-unit flag will now be set per NAL when preparing the buffer list to payload. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4937>
Without this patch all buffers that pass the payloader are marked as non-delta-unit buffers. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2969>