cipso: Fix documentation comment

The CIPSO protocol engine incorrectly stated that the FIPS-188 specification
could be found in the kernel's Documentation directory.  This patch corrects
that by removing the comment and directing users to the FIPS-188 documented
hosted online.  For the sake of completeness I've also included a link to the
CIPSO draft specification on the NetLabel website.

Thanks to Randy Dunlap for spotting the error and letting me know.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: James Morris <jmorris@namei.org>