src.ctf.lttng-live: honor component's initial log level and query LL

Except for `viewer-connection.c` which is pretty consistent in having a
named "viewer connection" instance in each function, the other files
deal with too many objects/concepts to have a systematic expression to
identify the log level, so they use local `log_level` variables.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I102408375d4d3d2df21c756b6581c642ece77ff1
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1494
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>