Can't hear anyone in voice calls

### Description

When voice chatting with one person, neither participant can hear each other. This has been tested with desktop/desktop, browser/browser, and desktop/browser with all combinations, including unchecking P2P for 1:1 calls and falling back to the turn.matrix.org TURN server.

One participant is on Linux Mint and the other is on Windows 10, and both participants have different public Matrix homeservers. Both the input and output devices look fine on both ends. E2E encryption is enabled for both users. For reference, voice calls on other communication platforms are working.

### Steps to reproduce

- Direct message another user to create a room with both participants.
- Attempt a voice call.
- The voice call starts, but neither participant can hear any audio.

Participants should be able to hear each other when the call starts if everything is configured properly.

Logs being sent: yes

### Version information

- **Platform**: Both

For the web app:

- **Browser**: Firefox 76.0 (64-bit)
- **OS**: Windows 10, Linux Mint 19.3 Tricia
- **URL**: https://riot.im/app/, https://riot.privacytools.io/

For the desktop app:

- **OS**: Windows 10, Linux Mint 19.3 Tricia
- **Version**: 1.6.2

Begin with the submitted debug logs and the voice-call behavior across the listed web and desktop combinations. Reproduce the direct-message call using Firefox 76, Windows 10, and Linux Mint 19.3, then compare the logs and verify completion when both participants can hear audio.

Written by the indexing model from the issue text.