net: Log to net debug in MaybeDiscourageAndDisconnect except for noban and manual peers

Summary:
The goal is to avoid local peers (e.g. untrusted peers on the local network or inbound onion peers via a local onion proxy) filling the debug log (and thus the disk).

This is a backport of core#20845

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13302