message: integration_tests: fix FTP server test
  We need to use the new add_any_connection API to make the server test
  pass.
diff: @@ -275,20 +275,19 @@ TEST(FtpTest, UploadFiles)
  TEST(FtpTest, TestServer)
  {
  - ConnectionResult ret;
  -
  Mavsdk mavsdk_gcs;
  Mavsdk::Configuration config_gcs(Mavsdk::Configuration::UsageType::GroundStation);
  mavsdk_gcs.set_configuration(config_gcs);
  - ret = mavsdk_gcs.add_udp_connection(24550);
  - ASSERT_EQ(ret, ConnectionResult::Success);
  - auto system_gcs = mavsdk_gcs.systems().at(0);
  + ASSERT_EQ(mavsdk_gcs.add_any_connection("udp://:24550"), ConnectionResult::Success);
  Mavsdk mavsdk_cc;
  Mavsdk::Configuration config_cc(Mavsdk::Configuration::UsageType::GroundStation);
  mavsdk_cc.set_configuration(config_cc);
  - ret = mavsdk_cc.setup_udp_remote("127.0.0.1", 24550);
  - ASSERT_EQ(ret, ConnectionResult::Success);
  + ASSERT_EQ(mavsdk_cc.add_any_connection("udp://127.0.0.1:24550"), ConnectionResult::Success);
  +
  + std::this_thread::sleep_for(std::chrono::seconds(1));
  +
  + auto system_gcs = mavsdk_gcs.systems().at(0);
  auto system_cc = mavsdk_cc.systems().at(0);
  auto mavlink_passthrough_cc = std::make_shared<MavlinkPassthrough>(system_cc);
  