This is not yet supported by virtiofsd.

Fixes #23 a.k.a. https://gitlab.com/libvirt/libvirt/-/issues/23Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>