net: Send post-verack handshake messages at most once

Summary:
There is no need to send SENDHEADERS and SENDCMPCT messages as a reply to each VERACK that is received. For alive checks, a PING/PONG can be used.

This is a backport of core#20146

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10469