The previous approach of using a simple pointer could lead to a use-after-free in case a data-channel was created and its parent webrtcbin was disposed soon after. Fixes #2103 Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4160>
Fixes a possible race where closing a data channel may produce e.g. not-linked errors. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3381>