New port: net/libmaxminddb

The libmaxminddb library provides a C library for reading MaxMind DB
files, including the GeoIP2 databases from MaxMind. This is a custom
binary format designed to facilitate fast lookups of IP addresses while
allowing for great flexibility in the type of data associated with an
address.

WWW: https://github.com/maxmind/libmaxminddb

PR: 197713
Submitted by: fullermd@over-yonder.net