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We don't handle `channelId` correctly

See original GitHub issue

Expected behavior

RTCPeerConnection pc = xxx;
const channel1 = pc.createDataChannel("label1", {maxRetransmits: 0, ordered: false});
channel1.onopen = xxx; // should be called
const channel2 = pc.createDataChannel("label2", {maxRetransmits: 0, ordered: false});
channel2.onopen = xxx; // should be called

Observerd behavior

Only first channel can receive state change event.

Steps to reproduce the problem

Just create multiple data channels in iOS, with react-native-webrtc >= 1.75.3

Platform information

React Native version: 0.63.3
Plugin version: 1.75.3
OS: iOS
OS version: 10

There is already a PR try to resolve this issue: https://github.com/react-native-webrtc/react-native-webrtc/pull/726 . However it didn’t fix the problem completely. Based on the discussion, I found that in the PR, aka commit f3736ed, those guys introduced checking for negotiated. If negotiated == false, id will be reset to -1. And in the following method AllocateSid, it will try to run potential_sid += 2;. So when - (void)dataChannelDidChangeState:(RTCDataChannel*)channel is called, channel.channelId had been changed, and different from what we recorded in peerConnection.dataChannels which is done in createDataChannel:(nonnull NSNumber *)peerConnectionId label:(NSString *)label config:(RTCDataChannelConfiguration *)config. This negotiated logic still exists in the newest master branch of webrtc.

Previously, our team used react-native-webrtc@1.69.2, which rely on [M69](https://github.com/jitsi/webrtc/tree/cb536cf7a368e77ec29a6779de7fbebf2c300b70), checking the datachannel.cc in that commit, there is not negotiated logic, so everything is happy back on that time.

This PR seems to work for one channel, because it changes the id generation to start from 1 instead of 0, which coincidently matches the id generated in webrtc sdk.

I don’t have enough knowledge on webrtc and negotiated flag. What should be a correct fix for this?

Currently, in order to be able to use multiple channels, you can try to manually assign ids to your data channels, start from 1, and +2 for each. Which means:

const channel1 = pc.createDataChannel("label1", {id: 1, maxRetransmits: 0, ordered: false});
const channel2 = pc.createDataChannel("label1", {id: 3, maxRetransmits: 0, ordered: false});
const channel3 = pc.createDataChannel("label1", {id: 5, maxRetransmits: 0, ordered: false});