kmsagnosticbin: improve source code

Change-Id: Icdd52e522c31470b52433dfa2e4ea04de026f169
kmsagnosticbin: drop buffers until key-frame after gap detection

Change-Id: Icac9ef2c9638d78593da0bf37e652907c2f9eba1
kmsbasertpendpoint: add rtcp-fb-nack-pli for caps

Change-Id: I1ed015c5e2ab950909410015731c607243b5bd90