message: config: fix comment
diff: @@ -205,7 +205,7 @@ public:
  typedef ConstSingleton<MetadataFilterValues> MetadataFilters;
  /**
  - * Keys for MetadataFilterConstants::ENVOY_LB metadata.
  + * Keys for MetadataFilterValues::ENVOY_LB metadata.
  */
  class MetadataEnvoyLbKeyValues {
  public:
  