sdp_utils: fix doc of sdp_utils_sdp_media_get_rtpmap

Change-Id: I38bcdc792efd8db155ed72f7f9e959312990980a
sdp_utils: add gst_sdp_media_format_get_encoding_name

Change-Id: I7c177c390047e02e694234c7ea5e7216883dc312
kmsbasertpendpoint: use constants for encoding names

Change-Id: I8a7978f22eece8707b67e523c66e2dca39cc7a08
kmswebrtcendpoint: add "rtcp-fb" attrs when needed

Change-Id: Iedc03797464027904e7751b2350c35c28e04f7de