[net processing] Move CNodeState declaration above PeerManagerImpl

Summary:
This is a partial backport of core#24543
https://github.com/bitcoin/bitcoin/pull/24543/commits/37ecaf3e7a028486a0a1c9b717e8eb4214215805

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14861