Fix restorevol crash on corrupt nDumpTimes value

If the number of dump times claimed in the volume header was greater
than MAXDUMPTIMES, restorevol would happily write over random stack
memory and crash.  Sanity-check the loaded value and cap it to
MAXDUMPTIMES with a warning.

Bug found by Mayhem and reported by Alexandre Rebert.

Change-Id: Ib0edd9b1b6f540d8b0128151333d3bb0a8ef37fa
Reviewed-on: http://gerrit.openafs.org/10025
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Fix restorevol sanity check on afs_int32

restorevol reads various values of different lengths into an
afs_int32 and does a sanity check to ensure that there is enough
room to store the desired value length.  However, the check was
done against the wrong variable, making it ineffective.

This check is unlikely to ever trigger, but fix it just in case.

Change-Id: Ia81bd9ff9a2ce8e2d93af384c8e8c664f5434d5e
Reviewed-on: http://gerrit.openafs.org/10026
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>