MINOR: stick-table: move the task_queue() call outside of the lock

The write lock in stktable_requeue_exp() is quite expensive and should
be shortened as much as possible. There's no need for it when calling
task_queue() so let's move it out.

On a 80-thread machine with a peers section, the request rate increased
from 368k to 397k rps.

src/stick_table.c

@@ -565,9 +565,9 @@ void stktable_requeue_exp(struct stktable *t, const struct stksess *ts)
 		new_exp = tick_first(expire, old_exp);
 	}
 
-	task_queue(t->exp_task);
-
 	HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &t->lock);
+
+	task_queue(t->exp_task);
 }
 
 /* Returns a valid or initialized stksess for the specified stktable_key in the