Merge #15824: docs: Improve netbase comments

Summary:
c7f6ce74d3a5cf2a0c5bac20eab1efd997175a72 docs: Improve netbase comments (Carl Dong)

Pull request description:

Second in a series of PRs documenting the net stack. Contributed with sincere thanks to sipa, laanwj, and gmaxwell for providing much of the history, context, and rationale.

ACKs for top commit:

laanwj:
  ACK c7f6ce74d3a5cf2a0c5bac20eab1efd997175a72

Tree-SHA512: ad83054d3b8d0c8c3fb55be011bcf294176e7509513bf61326866afd53e8159644e0d59bb3a2f404717f525cbf736096d4c1990e61cfd89845d51fa6b5394b7c

Backport of Core PR15824

Test Plan:

ninja

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6628