kset: move /sys/slab to /sys/kernel/slab

/sys/kernel is where these things should go.
Also updated the documentation and tool that used this directory.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>