Only set the RtcEventLog for media transport when it's used for media.
Only set the RtcEventLog for media transport when it's used for media.

Currently, GenerateOrGetLastMediaTransportOffer() creates a media
transport that has an RtcEventLog, regardless of whether the media
transport is used for media or data channels.  It should only set the
RtcEventLog when used for media.

Bug: webrtc:10789
Change-Id: Id91c16973deec89bbc8c6518c4c9f1039f1265fc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144367
Commit-Queue: Bjorn Mellem <fbd9b9fcff27ba9e617a0b2d416d05a7dfd43a01@webrtc.org>
Commit-Queue: Steve Anton <93f73658da16553b94c040887a439a155812e54e@webrtc.org>
Reviewed-by: Peter Slatala <7380603cea218c08053abc8e2257a75ccb7371d4@webrtc.org>
Reviewed-by: Steve Anton <93f73658da16553b94c040887a439a155812e54e@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28450}

ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc