RTPBaseDepayload.flush

If GstRTPBaseDepayload.process or GstRTPBaseDepayload.process_rtp_packet drop an output buffer this function tells the base class to flush header extension cache as well.

This will not drop an input RTP header marked as delayed from [gstrtp.rtpbase_depayload.RTPBaseDepayload.delayed].

If keep_current is true the current input RTP header will be kept and enqueued after flushing the previous input RTP headers.

A typical use-case for keep_current is when the depayloader implementation invalidates the current output buffer and starts a new one with the current RTP input buffer.

Must be called with the stream lock held.