CVE-2018-14629 dns: fix CNAME loop prevention using counter regression

CVE-2018-14629 dns: fix CNAME loop prevention using counter regression

The loop prevention should only be done for CNAME records!

Otherwise we truncate the answer records for A, AAAA or
SRV queries, which is a bad idea if you have more than 20 DCs.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13600

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Dec  4 08:52:29 CET 2018 on sn-devel-144

(cherry picked from commit 34f4491d79b47b2fe2457b8882f11644cf773bc4)

Autobuild-User(v4-7-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-7-test): Fri Dec  7 16:59:16 CET 2018 on sn-devel-144