message: Update net_processing WTXID documentation per BIP339
  as BIP339 currently states:
  "The wtxidrelay message MUST be sent in response to a version
  message from a peer whose protocol version is >= 70016 and
  prior to sending a verack. A wtxidrelay message received after
  a verack message MUST be ignored or treated as invalid."
diff: @@ -2500,8 +2500,8 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
  return;
  }
  - // Feature negotiation of wtxidrelay should happen between VERSION and
  - // VERACK, to avoid relay problems from switching after a connection is up
  + // Feature negotiation of wtxidrelay must happen between VERSION and VERACK
  + // to avoid relay problems from switching after a connection is up.
  if (msg_type == NetMsgType::WTXIDRELAY) {
  if (pfrom.fSuccessfullyConnected) {
  // Disconnect peers that send wtxidrelay message after VERACK; this
  