Backport of "webrtcbin: Limit sink query to sink pads" into 1.20
requested to merge tpm/gstreamer:backport-mr-2615-into-1.20-only-do-caps-query-on-sinkpads into 1.20
Backport of !2615 (merged) "webrtcbin: Limit sink query to sink pads".
Commits:
- c4971a45 webrtcbin: Limit sink query to sink pads