[Virtio-fs] [virtiofsd] MR merged: Fix st_mode of . and .. directories in readdirplus

[virtiofs-bot at sinrega.org]

Generally, `st_mode` (as a field of `struct stat`) is made of `S_IFDIR`,
`S_IFREG`, etc., but `d_type` (as a field of `struct dirent`) is made of
`DT_DIR`, `DT_REG`, etc. But these definitions are differ up to a 12 bit
shift.
It leads to incorrect attributes of `.` and `..` in Windows guest, so fix it.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2074311
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https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/111