libadmin/vos/vosutils.c: mask out sign-extension

Right-shifting a signed int by 24 bits can produce a value outside of
0..0xff due to sign-extension.  As a result, in AddressMatch(), the
first bPattern!=255 check can never succeed.  Fix by masking with 255
before comparison.

Reviewed-on: http://gerrit.openafs.org/8884
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 8e8e3c26b87d78b92d96ba91d58ee59d774ebcb5)

Change-Id: Ifee303905d004936e96f6be1e6a9188d7b70978c
Reviewed-on: http://gerrit.openafs.org/9517
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>