message: core: call the callbacks again
  This was fixed in the caller of these functions. The problem was that
  only a const reference of the callback was given, however this seems to
  be invalid later, so a copy by value is needed.
diff: @@ -335,8 +335,7 @@ void MavlinkParameters::process_param_ext_ack(const mavlink_message_t &message)
  if (param_ext_ack.param_result == PARAM_ACK_ACCEPTED) {
  // We are done, inform caller and go back to idle
  if (work.callback) {
  - // FIXME: this crashes in Android wrapper
  - //work.callback(true);
  + work.callback(true);
  }
  _request_state = RequestState::NONE;
  @@ -354,8 +353,7 @@ void MavlinkParameters::process_param_ext_ack(const mavlink_message_t &message)
  // We are done but unsuccessful
  // TODO: we need better error feedback
  if (work.callback) {
  - // FIXME: this crashes in Android wrapper
  - //work.callback(false);
  + work.callback(false);
  }
  _request_state = RequestState::NONE;
  