[refactor] Update GetAddr_() function signature

Summary:

Update so the internal function signature matches the external one, as is the case for the other addrman functions.

Partial backport of core#22950:
https://github.com/bitcoin/bitcoin/pull/22950/commits/14f9e000d05f82b364d5a142cafc70b10406b660

Depends on D12333.

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12334