VoIP example not triggering the call on sender's side

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**Describe the bug**
When running the VoIP example over 2 tabs and calling myself, the call stay in state "invite_sent" from the caller's side.
I logged the state changes of the call from both sides :

- Caller :

fledgling
wait_local_media
create_offer
invite_sent
ended

- Receiver:

ringing
wait_local_media
create_answer
connecting
connected
ended

Is the example outdated ?

**To Reproduce**
Steps to reproduce the behavior:
1. Run the VoIP example over 2 different ports, run it in 2 browsers
2. Try to call one browser from the other
3. Answer the call from the other browser
4. The call does not work

**Expected behavior**
The Caller receives an event to know the Callee has answered the call

**Additional context**
To log the call states I added to addListeners function :

> call.on("state", function (state, oldState) {
> console.warn("CALL STATE CHANGED", state, oldState)
> })

Start by running the VoIP example in two browsers on different ports and reproduce the caller and receiver state sequences described in the issue. Inspect the addListeners call-state logging and the signaling path around the caller remaining in invite_sent; done means the caller receives an event after the callee answers and the call proceeds normally.

Written by the indexing model from the issue text.