[addrman] Merge the two Add() functions

Summary:

Merge the two definitions of this overloaded function to reduce code duplication.

Backport of core#22627.

Depends on D12274.

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12275