log: Clarify that block request below NODE_NETWORK_LIMITED_MIN_BLOCKS disconnects

Summary:
This is a partial backport of core#21235
https://github.com/bitcoin/bitcoin/pull/21235/commits/fae7c0429f96e08bcac944f6fa30264636dfda8c

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13309