Fix a bug where the taskqueue kproc was being parented by init

because RFNOWAIT was being passed to kproc_create.

The result was that shutdown took quite a bit longer because this
errant "child" would not respond to termination signals from init
at system shutdown.

RFNOWAIT dissassociates itself from the caller by attaching to init
as a parent proc.  We could have had the taskqueue proc listen for
SIGKILL, but being able to SIGKILL a potentially critical system
process doesn't seem like a good idea.

sys/kern/subr_taskqueue.c

@@ -271,7 +271,7 @@ TASKQUEUE_DEFINE(swi_giant, taskqueue_swi_giant_enqueue, 0,
 
 TASKQUEUE_DEFINE(thread, taskqueue_thread_enqueue, 0,
 		 kthread_create(taskqueue_kthread, NULL,
-		 &taskqueue_thread_proc, RFNOWAIT, 0, "taskqueue"));
+		 &taskqueue_thread_proc, 0, 0, "taskqueue"));
 
 int
 taskqueue_enqueue_fast(struct taskqueue *queue, struct task *task)