virtio_net: Don't enable NAPI when interface is down

Commit 4e09ff53 ("virtio-net: disable NAPI only when enabled during
XDP set") tried to fix inappropriate NAPI enabling/disabling when
!netif_running(), but was not complete.

On error path virtio_net could enable NAPI even when !netif_running().
This can cause enabling NAPI twice on virtnet_open(), which would
trigger BUG_ON() in napi_enable().

Fixes: 4941d472 ("virtio-net: do not reset during XDP set")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -2430,8 +2430,10 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 	return 0;
 
 err:
-	for (i = 0; i < vi->max_queue_pairs; i++)
-		virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
+	if (netif_running(dev)) {
+		for (i = 0; i < vi->max_queue_pairs; i++)
+			virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
+	}
 	if (prog)
 		bpf_prog_sub(prog, vi->max_queue_pairs - 1);
 	return err;