DAFS: Do not ignore out-of-range -vhashsize

DAFS: Do not ignore out-of-range -vhashsize

If the specified -vhashsize is out of the 6-14 range, do not just
ignore it. Instead, note the error and quit.

Reviewed-on: http://gerrit.openafs.org/2649
Tested-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 575bdaf56e8f5503513bec113653fbbe525ae228)

Change-Id: Ie0ebfcf1b5c88816ef58eab109fb05de4c7fad1e
Reviewed-on: http://gerrit.openafs.org/5749
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>