net/openmdns: update 0.7 -> 0.9 and take maintenership

Changelog:

https://github.com/haesbaert/mdnsd/releases/tag/0.8
https://github.com/haesbaert/mdnsd/releases/tag/0.9

Major changes:

• Move mdnsl into a static libmdns library
• Silently ignore T_NULL RR records generated by legacy Airdrop on macOS
• Update rr_type_name to produce "NULL" as the name of type T_NULL(10)
• Allow us to reflect PTR packets between two interfaces/networks in the daemon.
• Fix RR leaks from cache_process()

Port changes:

• Reorder Makefile to make portlint happy
• Take port maintenership