message: Add comment explaining intended use of m_tx_relay
diff: @@ -733,6 +733,7 @@ public:
  int64_t nextSendTimeFeeFilter{0};
  };
  + // m_tx_relay == nullptr if we're not relaying transactions with this peer
  std::unique_ptr<TxRelay> m_tx_relay;
  // Used for headers announcements - unfiltered blocks to relay
  std::vector<uint256> vBlockHashesToAnnounce GUARDED_BY(cs_inventory);
  