Make config_item_type structures const as they are either passed to a
function having the argument as const or stored in the const "ci_type"
field of a config_item structure.

Done using Coccinelle.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Remove the old show_attribute and store_attribute methods and update
the documentation.  Also replace the two C samples with a single new
one in the proper samples directory where people expect to find it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>