zones deleted during asyncload are never freed
Zones that are deleted during the asyncload go into spiral:
dns_zone_create:::0:0x7f4c0b3c4e00->irefs = 0
zone_iattach:asyncload:zt.c:370:0x7f4c0b3c4e00->irefs = 2
dns_zone__idetach:zone_asyncload:zone.c:2423:0x7f4c0b3c4e00->irefs = 1
[...13k...]
zone_iattach:asyncload:zt.c:370:0x7f4c0b3c4e00->irefs = 2
dns_zone__idetach:zone_asyncload:zone.c:2423:0x7f4c0b3c4e00->irefs = 1
[...continues...]