xfs: pass the attr value to put_listent when possible

Pass the attr value to put_listent when we have local xattrs or
shortform xattrs.  This will enable the GETPARENTS ioctl to use
xfs_attr_list as its backend.

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>