NetLabel: add tag verification when adding new CIPSOv4 DOI definitions

Currently the CIPSOv4 engine does not do any sort of checking when a new DOI
definition is added.  The tags are still verified but only as a side effect of
normal NetLabel operation (packet processing, socket labeling, etc.) which
would cause application errors due to the faulty configuration.  This patch
adds tag checking when new DOI definition are added allowing us to catch these
configuration problems when they happen.

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