sdpmessage: Annotate SDP message parameters for `parse_uri()` and `parse_buffer(...

sdpmessage: Annotate SDP message parameters for `parse_uri()` and `parse_buffer()` correctly

They are not actually `out` parameters but must be allocated and
initialized to a valid SDP message by the caller. Just allocating them
without initialization will cause memory corruptions because the
functions will try to clear/append to the existing SDP message.

As such they should be just marked as `transfer none`.

Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1605

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3484>