Add dns/go-geodns: DNS server with per-client targeted responses

GeoDNS is a DNS server with per-client targeted responses. It powers the NTP
Pool system and other similar services.

WWW: https://github.com/abh/geodns

PR: 227492
Submitted by: Vinicius Zavam <egypcio@googlemail.com>
Differential Revision: https://reviews.freebsd.org/D15056