budb:  Avoid use of anonymous structures to determine size

Change-Id: Ife337e4e020a0450020f9ae641b1711435b936c4
Reviewed-on: http://gerrit.openafs.org/8153
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>