src.ctf.lttng-live: Add setter for stream iterator state for uniform logging

src.ctf.lttng-live: Add setter for stream iterator state for uniform logging

Debugging LTTng live issues is tricky and having clean and uniform
logging statement for each state transition is useful to understand the
current state a lttng-live source.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: Ifc334bbb2afe78f9ea57fe24b0ad3860b59b0640
Reviewed-on: https://review.lttng.org/c/babeltrace/+/6676
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>