[Virtio-fs] [virtiofsd] MR merged: Replace deprecated MAX with the associated constant on each type

[virtiofs-bot at sinrega.org]

Replace the deprecated form of std::<type>::MAX with the associated MAX constant on each type <type>::MAX.
For instance:
```rust
// deprecated way
let max = std::usize::MAX;

// intended way
let max = usize::MAX;
```

See https://doc.rust-lang.org/core/usize/constant.MAX.html
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https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/112