Fix RTprop overestimation due to off-by-one timestamp diff.

prrt/proto/processes/dataReceiver.c

@@ -303,8 +303,6 @@ void *receive_data_loop(void *ptr) {
 
             XlapTimeStampCycle(sock_ptr, kind, seqno, HandlePacketStart);
 
-            send_feedback(sock_ptr, remote, seqno, prrt_recv_timestamp, sentTimestamp, packetType);
-
             if (packetType == PACKET_TYPE_DATA) {
                 handle_data_packet(sock_ptr, packet);
             } else if (packetType == PACKET_TYPE_REDUNDANCY) {
@@ -312,6 +310,7 @@ void *receive_data_loop(void *ptr) {
             } else {
                 goto error;
             }
+            send_feedback(sock_ptr, remote, seqno, prrt_recv_timestamp, sentTimestamp, packetType);
             XlapTimeStampCycle(sock_ptr, kind, seqno, HandlePacketEnd);
         } else {
             PrrtPacket_print(packet);