salvager: Do not break cbks when salvaging parts

salvager: Do not break cbks when salvaging parts

When salvaging whole partitions / whole servers, the fileserver is
assumed to not be running. So only break callbacks if we are salvaging
a single volume. If we are salvaging a whole partition, do not tell
the fileserver to break callbacks on changed volumes, since the
fileserver will not be around and we will just hang.

Change-Id: Ia158d5a00574a6907b9b040510ef7d827a2ee05d
Reviewed-on: http://gerrit.openafs.org/2865
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>