src.ctf.lttng-live: `live_viewer_connection`: make `obj` first member

src.ctf.lttng-live: `live_viewer_connection`: make `obj` first member

This fixes a leak. The `bt_object` member must always be the first
because the internal API casts any `void *` parameter to `bt_object *`.
The object API was not getting the correct reference count here.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I15ccf573e0b7f5078d434852e915f90d685e65e1
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1832
Tested-by: jenkins <jenkins@lttng.org>