message: [feature-flags] do not enable all features when feature flags is enabled
  This commit adds a check for the value of feature flags enablement,
  and enable the features only when feature flags is not enabled.
diff: @@ -185,9 +185,12 @@ void ControllerOpenThread::Init(void)
  #endif
  #endif
  +#if !OTBR_ENABLE_FEATURE_FLAGS
  + // Bring up all features when feature flags is not supported.
  #if OTBR_ENABLE_NAT64
  otNat64SetEnabled(mInstance, /* aEnabled */ true);
  #endif
  +#endif // OTBR_ENABLE_FEATURE_FLAGS
  mThreadHelper = std::unique_ptr<otbr::agent::ThreadHelper>(new otbr::agent::ThreadHelper(mInstance, this));
  