Fix report timestamps (#305)

This is not really a bug but annoying to receivers of our reports. If
the ticker ticks, but then another packet is handled first, the
timestamp of the report (from the ticker) will be before the receive
timestamp of the last packet in the report. In that case, the report
contains a 0x1FFF value to indicate that the packet was received after
the report. However, we know the timestamp and can send it, if we take
the timstamp after entering the case branch. At that time, it is
guaranteed, that no additional packets can be added to the report.

Author: mengelbart

pkg/rfc8888/interceptor.go

@@ -169,7 +169,8 @@ func (s *SenderInterceptor) loop(writer interceptor.RTCPWriter) {
 			s.log.Tracef("got packet: %v", pkt)
 			s.recorder.AddPacket(pkt.arrival, pkt.ssrc, pkt.sequenceNumber, pkt.ecn)
 
-		case now := <-t.Ch():
+		case <-t.Ch():
+			now := s.now()
 			s.log.Tracef("report triggered at %v", now)
 			if writer == nil {
 				s.log.Trace("no writer added, continue")