[Virtio-fs] [virtiofsd] MR merged: Expand "map" type rule

[virtiofs-bot at sinrega.org]

The XattrMap "map" type must add  automatic rules,
depending on whether "key" is empty or not.

The rule ":map::prepend" must be expanded to:
:prefix::prepend:
:bad:all::

The rule ":map:key:prepend" must be expanded to
:prefix:all:key:prepend:
:bad:server::key:
:bad:client:prepend::
:ok:all::

Closes #40
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https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/103