message: Add missing Stop method.
diff: @@ -35,6 +35,19 @@ public:
  return grpc::Status::OK;
  }
  + grpc::Status Stop(grpc::ServerContext * /* context */,
  + const rpc::Offboard::StopRequest * /* request */,
  + rpc::Offboard::StopResponse *response) override
  + {
  + auto offboard_result = _offboard.stop();
  +
  + if (response != nullptr) {
  + fillResponseWithResult(response, offboard_result);
  + }
  +
  + return grpc::Status::OK;
  + }
  +
  grpc::Status IsActive(grpc::ServerContext * /* context */,
  const rpc::Offboard::IsActiveRequest * /* request */,
  rpc::Offboard::IsActiveResponse *response) override
  