ristsink and rtpsink: set sync off on rtcp_sink
When using the following setup (the error can be reproduced using simpler sender pipelines), the receiver resynchronises the clock on RTCP packets. The effect was that a couple seconds were cut out of the playback because an initial RTCP packet was dropped.
When sending out all RTCP packets (setting sync=FALSE on the RTCP updsink), the playback is fine.
This syncs rtpsink with rtpsrc (where this property was already set).
gst-launch-1.0 filesrc location=899-en.mp3
! mpegaudioparse
! mpg123audiodec
! audioconvert
! audioresample
! avenc_g722
! rtpg722pay
! rtpsink uri=rtp://239.1.2.3:1234
gst-launch-1.0 uridecodebin rtp://239.1.2.3:1234?encoding-name=G722
! autoaudiosink