xen-netback: delete NAPI instance when queue fails to initialize

When xenvif_connect() fails it may leave a stale NAPI instance added to
the device.  Make sure we delete it in the error path.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/interface.c

@@ -615,6 +615,7 @@ err_tx_unbind:
 	queue->tx_irq = 0;
 err_unmap:
 	xenvif_unmap_frontend_rings(queue);
+	netif_napi_del(&queue->napi);
 err:
 	module_put(THIS_MODULE);
 	return err;