Windows: report AllocationSize in 1KB increments

Windows expects storage to be allocated in increments of some
block size.  The AFS servers allocate in 1K units so lets report
that to Windows.

Change-Id: I64ad1844339357733933cd9e360551fdcd450146
Reviewed-on: http://gerrit.openafs.org/11490
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>