Fallback to EDNS or TCP can be in conflict with test cases

[matsduf]

https://github.com/zonemaster/zonemaster-engine/blob/master/lib/Zonemaster/Engine/Profile.pm#L588-L597 says

resolver.defaults.fallback A boolean. If true, UDP queries that get responses with the C<TC> flag set will be automatically resent over TCP or using EDNS. Default true. In ldns-1.7.0 (NLnet Labs), in case of truncated answer when UDP is used, the same query is resent with EDNS0 and TCP (if needed). If you want the original answer (with TC bit set) and avoid this kind of replay, set this flag to false.

I am not sure that this should be configurable here, since this can be in conflict with the test cases. It is probably more reasonable that it is set to false in the calls to LDNS, and then handled by the Zonemaster code.