Bug 911055 - [zffos1.1][P3][Dailer]DuT doesn allow to dial a <<pause>>

We should put the constants here instead. Something like this:
```js
// DTMF control digit separator length (ms) as defined in GSM ETSI GSM 02.07
const DTMF_SEPARATOR_PAUSE_DURATION = 3000;
// comment this
const DTMF_PLAY_LENGTH = 120;
```