Assuming that V4L2 CAPTURE devices always use one buffer per JPEG image, we can always mark JPEGs provided by a V4L2 element as parsed. The V4L2 elements require that JPEG images sent to V4L2 OUTPUT devices must always be parsed. This is necessary to link a V4L2 CAPTURE device with a V4L2 OUTPUT device without explicitly marking the stream as parsed or adding a jpegparse into the pipeline. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4229>