xfs: check shortform attr entry flags specifically

While reviewing flag checking in the attr scrub functions, we noticed
that the shortform attr scanner didn't catch entries that have the LOCAL
or INCOMPLETE bits set.  Neither of these flags can ever be set on a
shortform attr, so we need to check this narrower set of valid flags.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>