Add asmap utility which queries a mapping

Summary:

The scripts for creating a compact IP->ASN mapping are here:
https://github.com/sipa/asmap

Partial backport 1/4 of core PR16702:
https://github.com/bitcoin/bitcoin/pull/16702/commits/8feb4e4b667361bf23344149c01594abebd56fdb

Test Plan:

ninja

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D8194