Merge #15824: docs: Improve netbase comments

c7f6ce7 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 c7f6ce7

Tree-SHA512: ad83054d3b8d0c8c3fb55be011bcf294176e7509513bf61326866afd53e8159644e0d59bb3a2f404717f525cbf736096d4c1990e61cfd89845d51fa6b5394b7c

Author: laanwj