Move the max records option in the AXFR code from ixfrdist to the AXFRRetriever class

[pieterlexis]

Short description

In #6872, a feature was added to ixfrdist whereby the total number of records accept in a single AXFR transaction can be limited. It makes sense to move this code to a central location like the AXFRRetriever for reuse in the auth and the recursor (RPZ).

Usecase

We might want to limit the amount of incoming records.