auditU: also report for rxkad-always-encrypt

The logic that works for security index 2 also works for index 3.

While here, update a comment in preparation for rxgk.

Change-Id: Ifd868fa8d9d0ba2f422fa1fac43e4f583d27a1ff
Reviewed-on: http://gerrit.openafs.org/10527
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: D Brashear <shadow@your-file-system.com>