DAFS: Clear salvage stats on VOL_DONE

DAFS: Clear salvage stats on VOL_DONE

When we VOL_DONE a volume, the volume has been deleted, so the salvage
stats/information are no longer relevant. Clear them out, so we don't
think the volume is still salvaging.

Reviewed-on: http://gerrit.openafs.org/4120
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 40049c56791f3488640ae65c5dc5c4d6503375bd)

Change-Id: I1c7f61994b050de7bd8c0e7fc39df978a31530a6
Reviewed-on: http://gerrit.openafs.org/4166
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>