virtiofsd (rust): Avoid use of deprecated '-o' for specifying options

Software environment

• libvirt version: 9.0.0

Description of problem

The rust version of virtiofsd considers use of the -o option deprecated, thus libvirt should not use them any more when the new daemon is in use:

$ /usr/libexec/virtiofsd --help
virtiofsd backend 1.4.0
Launch a virtiofsd backend.

USAGE:
    virtiofsd [FLAGS] [OPTIONS] --fd <fd> --socket <socket> --socket-path <socket-path>

[ ---- snipped ---- ]

OPTIONS:
        --cache <cache>
            The caching policy the file system should use (auto, always, never) [default: auto]

    -o <compat-options>...
            Options in a format compatible with the legacy implementation [deprecated]