The upload-pack program, when talking over v2, accepted the
packfile-uris protocol extension from the client, even if it did
not advertise the capability, which has been corrected.

* jk/upload-pack-v2-capability-cleanup:
  upload-pack: only accept packfile-uris if we advertised it
  upload-pack: use existing config mechanism for advertisement
  upload-pack: centralize setup of sideband-all config
  upload-pack: use repository struct to get config