Bug 1094878 - Call is not on hold anymore after hanging up another call even though the icon says it is

Passing a bool into a function like this is a bit ugly and unclear on first glance. I think it would be better here to add a function like this:
```js
function holdOrResumeCallByUser() {
  isCallHeldByUser = !!telephony.active;
  holdOrResumeSingleCall();
}
```