This patch adds a field trial for appending an extra
attribute which contains the remote ufrag for the permission.
The attribute is put into the comprehension-optional range
so that a TURN server should ignore it if it doesn't know if.
https://tools.ietf.org/html/rfc5389#section-18.2
Bug: webrtc:10350
Change-Id: I7d62ab94e947bddd670d8eb53d4ff89b1d1e275c
Reviewed-on: https://webrtc-review.googlesource.com/c/123901
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26859}