common/casefold: only check for the Casefold flag

common/casefold: only check for the Casefold flag

The _casefold_lsattr_dir function lists all of the file attributes.
As result, tests/generic/556.out has an ext4-specific assumption
that the test directories will have the Extents attribute. That
won't be true for all file systems, and it won't even be true for
ext4 file systems that do not have the extents feature enabled.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>