MINOR: listener: make the wait paths cleaner and more reliable

MINOR: listener: make the wait paths cleaner and more reliable

In listener_accept() there are several situations where we have to wait
for an event or a delay. These ones all implement their own call to
limit_listener() and the associated task_schedule(). In addition to
being ugly and confusing, one expire date computation is even wrong as
it doesn't take in account the fact that we're using threads and that
the value might change in the middle. Fortunately task_schedule() gets
it right for us.

This patch creates two jump locations, one for the global queue and
one for the proxy queue, allowing the rest of the code to only compute
the expire delay and jump to the right location.