Windows: Add caching to cm_GetAddrsU

Cache the results of VL_GetAddrsU queries and reuse the results
for subsequent calls when possible.

Reviewed-on: http://gerrit.openafs.org/10764
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 3b5c636480cda73938a532ffd079ba040907f78f)

Change-Id: Id81e3dae43ca514098c9bf677c79dc3e88e6a224
Reviewed-on: http://gerrit.openafs.org/10780
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>