missing `netdev user` support

It seems qemu-xpack-riscv  (as per 8.2.2) doesn't support `-netdev user` option:

```
qemu-system-riscv64: -netdev user,id=u1,hostfwd=tcp:127.0.0.1:10064-10.0.2.15:23: network backend 'user' is not compiled into this binary
```

Can this be added in future releases?

