message: failure: subscribe to param changes
  Without this we don't get the update if the param is set right before
  using the failure injection.
diff: @@ -18,8 +18,10 @@ void FailureImpl::deinit() {}
  void FailureImpl::enable()
  {
  + constexpr auto param_name = "SYS_FAILURE_EN";
  +
  _parent->get_param_int_async(
  - "SYS_FAILURE_EN",
  + param_name,
  [this](MAVLinkParameters::Result result, int32_t value) {
  if (result == MAVLinkParameters::Result::Success) {
  if (value == 1) {
  @@ -34,6 +36,19 @@ void FailureImpl::enable()
  }
  },
  this);
  +
  + _parent->subscribe_param_int(
  + param_name,
  + [this](int value) {
  + if (value == 1) {
  + _enabled = EnabledState::Enabled;
  + } else if (value == 0) {
  + _enabled = EnabledState::Disabled;
  + } else {
  + _enabled = EnabledState::Unknown;
  + }
  + },
  + this);
  }
  void FailureImpl::disable()
  