…stead (#5339)

## Issue being fixed or feature implemented
This refactoring is a follow-up changes to backport bitcoin#17164 (PR
#5314)

These changes are reduce difference in implementation for our code and
bitcoin's


## What was done?
Removed a flag m_block_relay_peer. Instead I call IsAddrRelayPeer() that
has same information now.
It changes logic introduced in #4888 due to dash-specific code.


## How Has This Been Tested?
Run unit/functional tests.

## Breaking Changes
No breaking changes

## Checklist:
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [x] I have made corresponding changes to the documentation
- [x] I have assigned this pull request to a milestone

comment was moved to net.h in 678df63 (dashpay#4888) and removed entirely in
796353a (dashpay#5771). the comment is being restored back to where it is
upstream, in CNode::RelayAddrsWithConn.

Dash uses a lot more CNode::RelayAddrsWithConn checks than Bitcoin (esp.
since a483122 (dashpay#4888)), so bitcoin#21186 will not adequately cover the
removal of RelayAddrsWithConn usages.

When possible to query with RelayAddrsWithPeer, that should be used, as
that value is the most reliable, else we rely on the former mutual
exclusivity of IsBlockOnlyConn and RelayAddrsWithConn to fill in the
blanks where a more reliable query isn't available.

Note: To prevent builds from breaking, a change has been made in
InstantSend code despite it breaking functionality. A commit later will
repair it by creating a way to access RelayAddrsWithPeer.