[Virtio-fs] [virtiofsd-rs] Issue opened: Virtiofsd panic when reaching max open descriptor.

[virtiofs-bot at sinrega.org]

Virtiofsd reports correctly "too many open files" to the guest until some value, after reaching this point it will just panic with the following message:
```
[...]
[2021-10-12T11:46:16Z DEBUG virtiofsd_rs] QUEUE_EVENT
thread 'vring_worker' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 24, kind: Uncategorized, message: "Too many open files"}
```

I think the correct behavior would be to continue the error report to the guest while the guest OS tries to open file descriptors without panicking.

I didn't see any other error related to this limit in the debug logs. Reporting such OS error in the debug log might be interesting?

virtiofsd-rs was launched using the following parameters:
```
virtiofsd-rs --socket=/path/to/socket --shared-dir=/path/to/dir --cache=never --sandbox=chroot --log-level=debug 2> "$VIRTIOFSD_LOG"
```

The issue can be reproduced consistently every time on my setup, before hitting that limit everything works fine.
---
https://gitlab.com/virtio-fs/virtiofsd-rs/-/issues/15