webrtc: Helper function openChannelPair is missing

[alvestrand]

7799ef9 introduced usage of a new helper called openChannelPair, but did not include the new helper in the commit.

This caused a test to fail:

https://wpt.fyi/results/webrtc/RTCDataChannel-id.html?label=master&label=experimental&aligned

Tracking Chrome bug: https://issues.chromium.org/457527819

[ManishKalsariya]

hello, my self Manish Kalsariya. currently persuing my B.Tech electrical engineering degree from NIT-Surat.I am completely fresher in open source contributions. can anyone help. actually don't know where to connect with people that's why i messaged here