The Zerofs nbd-client persist option does not work when the Zerofs server restarts.

The Zerofs nbd-client persist option does not work when the Zerofs server restarts, although I had added persist, but ifthe  server restarts file system will be read-only 
* Zerofs version

```code
0.15.6
```

* nbd-client options

```code
nbd-client 127.0.0.1 10809 /dev/nbd1 -N database -persist -timeout 600 -connections 4
```