[net/refactor] Extract m_addr_known logic from initializer list

Summary:
Partial backport (6/19) of core PR19316:
https://github.com/bitcoin/bitcoin/pull/19316/commits/af59feb05235ecb85ec9d75b09c66e71268c9889

Depends on D8715.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8716