Two new socket options are introduced OPT_SEND_ECN used for setting ECN bits. OPT_RECV_ECN used for reading the ECN bits. If ECN bits are set on received IP packets, ECT(1) and CE is propagated via rtc::ReceivedPacket. Bug: webrtc:15368 Change-Id: I3ac335007e2f7d30564569bbc80ce47fa541bef1 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/332380 Reviewed-by: Jonas Oreland <jonaso@google.com> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Per Kjellander <perkj@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41885}