freebsd_network: Implement taskqueue_drain_all.

Required by FreeBSD 12's iprowifi4965.

src/libs/compat/freebsd_network/compat/sys/taskqueue.h

@@ -32,6 +32,7 @@ void taskqueue_free(struct taskqueue *tq);
 void taskqueue_drain(struct taskqueue *tq, struct task *task);
 void taskqueue_drain_timeout(struct taskqueue *queue,
 	struct timeout_task *timeout_task);
+void taskqueue_drain_all(struct taskqueue *tq);
 void taskqueue_block(struct taskqueue *queue);
 void taskqueue_unblock(struct taskqueue *queue);
 int taskqueue_enqueue(struct taskqueue *tq, struct task *task);

src/libs/compat/freebsd_network/taskqueue.c

@@ -293,6 +293,28 @@ taskqueue_drain_timeout(struct taskqueue *queue,
 }
 
 
+static void
+taskqueue_task_nop_fn(void* context, int pending)
+{
+}
+
+
+void
+taskqueue_drain_all(struct taskqueue *taskQueue)
+{
+	struct task t_barrier;
+
+	if (taskQueue == NULL) {
+		printf("taskqueue_drain_all called with NULL taskqueue\n");
+		return;
+	}
+
+	TASK_INIT(&t_barrier, USHRT_MAX, taskqueue_task_nop_fn, &t_barrier);
+	taskqueue_enqueue(taskQueue, &t_barrier);
+	taskqueue_drain(taskQueue, &t_barrier);
+}
+
+
 static void
 taskqueue_enqueue_locked(struct taskqueue *taskQueue, struct task *task,
 	cpu_status status)