Long gap between accepting voice call and actual call starting

### Steps to reproduce

1. I have my phone with screen off
2. I also have Element Web open on my Computer
3. A phone call is incoming
4. My phone rings and Element Web shows a couple buttons with "accept" and "dismiss" and a timeout going on
5. I answer the call from my phone but until the Element Web popup times out we cannot hear each other on phone

### Outcome

#### What did you expect?

I'd expect the call to be accepted and working the moment I tap the green button on Element Android and Element Web to ack that or just let it be.

#### What happened instead?

It happens that we can't hear each other for a few seconds from when the call is accepted on phone

### Your phone model

XIAOMI Redmi 6A

### Operating system version

Android 9.1

### Application version and app store

Element 1.4.27, OLM 3.2.12 from Google Play Store

### Homeserver

Synapse version: 1.62.0

### Will you send logs?

No

### Are you willing to provide a PR?

No