Make sure that listxattr() returns zero and that getxattr() returns
ENODATA when no extended attributs are set. Use /sys/kernel/warn_count
as that always exists and is a read-only file.
Link: https://lore.kernel.org/20250702-hochmoderne-abklatsch-af9c605b57b2@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
