check_site.sh and site.sh were setting GLUON_SITE_CONFIG on their own
even though the environment variable was already exported.

Link to hackint.org added

The u-boot package has some issues causing its build to fail under certain
circumstances. As we don't support the ZyXEL devices it's used for anyways, just
don't build it anymore.

This now includes the previously added patch.

gluon-batman-on-wan: docs

If a given commit is not included in the master branch, the update script fails.