[Virtio-fs] [virtiofsd-rs] MR opened: Drop capabilties and don't announce KILLPRIV

[virtiofs-bot at sinrega.org]

This series introduces the ability to drop the capabilities before starting the service, and also stops announcing KILLPRIV support, which we never really supported.

This changes set up the stage for the upcoming KILLPRIV_V2 support.
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https://gitlab.com/virtio-fs/virtiofsd-rs/-/merge_requests/44