virtio: Dont add "config" to list for !per_vq_vector

For the MSI but non-per_vq_vector case, the config/change vq
also gets added to the list of vqs that need to process the
MSI interrupt. This is not needed as config has it's own
handler (vp_config_changed). In any case, vring_interrupt()
finds nothing needs to be done on this vq.

I tested this patch by testing the "Fallback:" and "Finally
fall back" cases in vp_find_vqs(). Please review.
Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/virtio/virtio_pci.c

@@ -415,9 +415,13 @@ static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index,
 		}
 	}
 
-	spin_lock_irqsave(&vp_dev->lock, flags);
-	list_add(&info->node, &vp_dev->virtqueues);
-	spin_unlock_irqrestore(&vp_dev->lock, flags);
+	if (callback) {
+		spin_lock_irqsave(&vp_dev->lock, flags);
+		list_add(&info->node, &vp_dev->virtqueues);
+		spin_unlock_irqrestore(&vp_dev->lock, flags);
+	} else {
+		INIT_LIST_HEAD(&info->node);
+	}
 
 	return vq;