net/posadis, another DNS server implementation

Add a new port - net/posadis. It is a new DNS server
implementation being actively developed at SourceForge.

Posadis is a DNS server project with the goal to create a
free, reliable, portable, fast, lightweight, easy to use,
standards compliant, and functionally complete, Domain Name
System server implementation.

PR: ports/48872
Submitted by: Sergei Kolobov <sergei@kolobov.com>