xfs: do not use logged xattr updates on V4 filesystems

V4 superblocks do not contain the log_incompat feature bit, which means
that we cannot protect xattr log items against kernels that are too old
to know how to recover them.  Turn off the log items for such
filesystems and adjust the "delayed" name to reflect what it's really
controlling.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>