message: Add missing comparison operators
diff: @@ -58,6 +58,16 @@ struct down_msg {
  error reason;
  };
  +/// @relates down_msg
  +inline bool operator==(const down_msg& x, const down_msg& y) noexcept {
  + return x.source == y.source && x.reason == y.reason;
  +}
  +
  +/// @relates down_msg
  +inline bool operator!=(const down_msg& x, const down_msg& y) noexcept {
  + return !(x == y);
  +}
  +
  /// @relates down_msg
  template <class Inspector>
  typename Inspector::result_type inspect(Inspector& f, down_msg& x) {
  