Fix bind DLZ module to prevent zone transfers for everyone

[github at samba.org]

New comment by littlejawa on Samba Github repository

https://github.com/samba-team/samba/pull/213#issuecomment-447762387
Comment:
Hi @abartlet ,
I made a merge request on gitlab here: https://gitlab.com/samba-team/samba/merge_requests/169.

I can extend the test cases as needed, just not sure how - can we discuss it on the gitlab thread?