hv_netvsc: cancel subchannel setup before halting device

Block setup of multiple channels earlier in the teardown
process. This avoids possible races between halt and subchannel
initialization.
Suggested-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/rndis_filter.c

@@ -1340,6 +1340,9 @@ void rndis_filter_device_remove(struct hv_device *dev,
 {
 	struct rndis_device *rndis_dev = net_dev->extension;
 
+	/* Don't try and setup sub channels if about to halt */
+	cancel_work_sync(&net_dev->subchan_work);
+
 	/* Halt and release the rndis device */
 	rndis_filter_halt_device(rndis_dev);