Change the source package name of the module source

Change the source package name of the module source

* Change the source package name of the stripped package generated by
  openafs-modules-source so that, should someone build a Debian source
  package from it, it won't have the same name as the main openafs
  source package.

(cherry picked from commit ce99915567a2f37f8d1006b20c4e4b0125208a4d)