This moves the construction of StunMessage instances for
ConnectionRequest, outside of the Prepare() method.
Following this, removing Construct()+Prepare() is relatively
straight forward.
Bug: none
Change-Id: Ibcf0510cef30a6e648005b43602c7ae1fb06729e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264558
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37122}
e83500e17b