Fix: controller: initial timeout for fencing callback takes any priority fencing delay into account

It's usually not necessary under normal circumstances since the timeout
for the async callback gets updated very soon with
st_client.c:update_callback_timeout() once fencer has decided the total
fencing timeout and reported it back to controller with
fenced_remote.c:report_timeout_period(). But anyway it makes sense to
be added for the initial.