Issue title: Cannot connect more than one vehicle on current master.
 Issue body: The output shows QGC connecting but the UI does not reflect multiple connections.

```
LinkManagerLog: New heartbeat on link:vehicleId:vehicleMavlinkVersion:vehicleFirmwareType:vehicleType  "/dev/cu.usbmodem1" 1 3 12 1
LinkManagerLog: New heartbeat on link:vehicleId:vehicleMavlinkVersion:vehicleFirmwareType:vehicleType  "Default UDP Link" 1 3 12 2
```

The UI only shows the USB link. There is no way to see the one connected on UDP.

 Comments: 
 Comment 0: Are you sure your vehicles don't have the same id?
 Comment 1: Crap. I changed the wrong ID on all 3 vehicles. I changed Comp ID instead of Sys ID. Tired...

{'source': 'GithubIssues', 'repo_name_with_owner': 'mavlink/qgroundcontrol', 'issue_id': 126966026, 'repo_stars': 2313.0}