IPoIB: Avoid flushing the driver workqueue on dev_down

The driver should not flush the whole workqueue when only one work (the
pkey poll one) needs to be cancelled.  Use cancel_delayed_work_sync()
instead.
Signed-off-by: NErez Shitrit <erezsh@mellanox.com>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NRoland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib_ib.c

@@ -749,10 +749,8 @@ int ipoib_ib_dev_down(struct net_device *dev, int flush)
 	if (!test_bit(IPOIB_PKEY_ASSIGNED, &priv->flags)) {
 		mutex_lock(&pkey_mutex);
 		set_bit(IPOIB_PKEY_STOP, &priv->flags);
-		cancel_delayed_work(&priv->pkey_poll_task);
+		cancel_delayed_work_sync(&priv->pkey_poll_task);
 		mutex_unlock(&pkey_mutex);
-		if (flush)
-			flush_workqueue(ipoib_workqueue);
 	}
 
 	ipoib_mcast_stop_thread(dev, flush);