BUG/MINOR: listener: renice the accept ring processing task

It is not acceptable that the accept queues are handled with a normal
priority since they are supposed to quickly dispatch the incoming
traffic, resulting in tasks which will have their respective nice
values and place in the queue. Let's renice the accept ring tasks
to -1024.

No backport is needed, this is strictly 2.0.

src/listener.c

@@ -201,6 +201,7 @@ static int accept_queue_init()
 			ha_alert("Out of memory while initializing accept queue for thread %d\n", i);
 			return ERR_FATAL|ERR_ABORT;
 		}
+		t->nice = -1024;
 		t->process = accept_queue_process;
 		t->context = &accept_queue_rings[i];
 		accept_queue_rings[i].task = t;