message: [refactor] Simplify check for block-relay-only connection.
  Previously we deduced it was a block-relay-only based on presence of the
  m_tx_relay structure. Now we have the ability to identify it directly via a
  connection type accessor function.
diff: @@ -2025,7 +2025,7 @@ static void ProcessHeadersMessage(CNode& pfrom, CConnman& connman, ChainstateMan
  }
  }
  - if (!pfrom.fDisconnect && pfrom.IsOutboundOrBlockRelayConn() && nodestate->pindexBestKnownBlock != nullptr && pfrom.m_tx_relay != nullptr) {
  + if (!pfrom.fDisconnect && pfrom.IsFullOutboundConn() && nodestate->pindexBestKnownBlock != nullptr) {
  // If this is an outbound full-relay peer, check to see if we should protect
  // it from the bad/lagging chain logic.
  // Note that block-relay-only peers are already implicitly protected, so we
  