Windows: correct CheckOfflineVolumeState logic

Windows: correct CheckOfflineVolumeState logic

Do not blindly set the return 'online' state to TRUE if
the state has not in fact changed.

Do not blindly clear the 'alldown' flag without checking the
actual 'down' state of the file server.

Reviewed-on: http://gerrit.openafs.org/5323
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 8d4f65c3021b3416d290a1d5f1e8e61d14a936c7)

Change-Id: I96cd543480dd87f0998e36fd43deebd2142db1a0
Reviewed-on: http://gerrit.openafs.org/5324
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>