This allows downstream (payloaders mostly) to be able to correctly detect actual packet loss from rtp sequence numbers. See https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/issues/581 for background. Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1407 Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3212>