vos: free ubulkentries with xdr_free

vos: free ubulkentries with xdr_free

Instead of using free() to free the ubulkentries data structure
use xdr_free().

Reviewed-on: http://gerrit.openafs.org/3590
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit a7836dda8c1aab18c937c7e8909d4d9a678a53fa)

Change-Id: I9af8aee92e0e187923ccd952a5487ea419446720
Reviewed-on: http://gerrit.openafs.org/3626
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>