in some configurations, samba stores NTFS-ACLs in this xattr[0], so
we should backup (if we can)
altough the 'security' namespace is special (e.g. in use by
selinux, etc.) this value is normally only used by samba and we
should be able to back it up.
to restore it, the user needs at least 'CAP_SYS_ADMIN' rights, otherwise
it cannot be set
0: https://www.samba.org/samba/docs/current/man-html/vfs_acl_xattr.8.html
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>