message: fix application error code
  Summary:
  ```
  s/quic::ApplicationErrorCode::STOPPING/GenericApplicationErrorCode::UNKNOWN/g
  ```
diff: @@ -119,13 +119,13 @@ class QuicStreamAsyncTransport : public folly::AsyncTransportWrapper,
  if (writeBuf_.empty()) {
  close();
  } else {
  - sock_->resetStream(id_, quic::ApplicationErrorCode::STOPPING);
  + sock_->resetStream(id_, quic::GenericApplicationErrorCode::UNKNOWN);
  VLOG(4) << "Reset stream from closeNow";
  }
  }
  void closeWithReset() override {
  - sock_->resetStream(id_, quic::ApplicationErrorCode::STOPPING);
  + sock_->resetStream(id_, quic::GenericApplicationErrorCode::UNKNOWN);
  VLOG(4) << "Reset stream from closeWithReset";
  }
  