message: telemetry: add missing message handler registry
  Without this we never receive the IMU message and the integration test
  fails.
diff: @@ -68,6 +68,11 @@ void TelemetryImpl::init()
  _parent->register_mavlink_message_handler(
  MAVLINK_MSG_ID_RC_CHANNELS, std::bind(&TelemetryImpl::process_rc_channels, this, _1), this);
  + _parent->register_mavlink_message_handler(
  + MAVLINK_MSG_ID_HIGHRES_IMU,
  + std::bind(&TelemetryImpl::process_imu_reading_ned, this, _1),
  + this);
  +
  _parent->register_param_changed_handler(
  std::bind(&TelemetryImpl::process_parameter_update, this, _1), this);
  }
  