Adds default for PeerConnectionObserver::OnIceConnectionChange
Adds default for PeerConnectionObserver::OnIceConnectionChange

It's planned to be deprecated so it should not be required.

Bug: webrtc:9883
Change-Id: I7daa922786d3cbf6bca38e205f4f57773f3f8448
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/147275
Commit-Queue: Sebastian Jansson <c24d1bc144eb7c11e553f59153fa17dba85ca83e@webrtc.org>
Reviewed-by: Henrik Boström <106ab6647ddadbf38d6259e9d5ec4de77fa52c00@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28715}

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