volser: -log restore operations

Add vos restore to the list of operations which are logged
when the volserver is running with the -log option. Example
log line:

    admin on 172.16.50.141 is executing Restore 536870969

Change-Id: Ia6eb07258831865dfe2c85d1b9df078f33c4b640
Reviewed-on: http://gerrit.openafs.org/9926
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>