Update net/dnsdist to 1.2.0.

- fix for CVE-2016-7069 and CVE-2017-7557.
- applying rules on cache hits
- addition of runtime changeable rules that matches IP address for a
  certain time: TimedIPSetRule
- SNMP support, exporting statistics and sending traps
- preventing the packet cache from ageing responses when deployed in
  front of authoritative servers
- TTL alteration capabilities
- consistent hash results over multiple deployments
- exporting CNAME records over protobuf
- tuning the size of the ringbuffers used to keep track of recent
  queries and responses
- various DNSCrypt-related fixes and improvements, including automatic
  key rotation

Full changelog:

  https://dnsdist.org/changelog.html

(fhajny)