net: qrtr: Stop rx_worker before freeing node

As the endpoint is unregistered there might still be work pending to
handle incoming messages, which will result in a use after free
scenario. The plan is to remove the rx_worker, but until then (and for
stable@) ensure that the work is stopped before the node is freed.

Fixes: bdabad3e36 ("net: Add Qualcomm IPC router")
Cc: stable@vger.kernel.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

net/qrtr/qrtr.c

@@ -150,6 +150,7 @@ static void __qrtr_node_release(struct kref *kref)
 	list_del(&node->item);
 	mutex_unlock(&qrtr_node_lock);
 
+	cancel_work_sync(&node->work);
 	skb_queue_purge(&node->rx_queue);
 	kfree(node);
 }