res_rtp_asterisk: Fix sequence number cycling and packet loss count.

This change fixes two bugs which both resulted in the packet loss
count exceeding 65,000.

The first issue is that the sequence number check to determine if
cycling had occurred was using the wrong variable resulting in the
check never seeing that cycling has occurred, throwing off the
packet loss calculation. It now uses the correct variable.

The second issue is that the packet loss calculation assumed that
the received number of packets in an interval could never exceed
the expected number. In practice this isn't true due to delayed
or retransmitted packets. The expected will now be updated to
the received number if the received exceeds it.

ASTERISK-28379

Change-Id: If888ebc194ab69ac3194113a808c414b014ce0f6

res/res_rtp_asterisk.c

@@ -4126,6 +4126,14 @@ static void calculate_lost_packet_statistics(struct ast_rtp *rtp,
 	*lost_packets = expected_packets - rtp->rxcount;
 	expected_interval = expected_packets - rtp->rtcp->expected_prior;
 	received_interval = rtp->rxcount - rtp->rtcp->received_prior;
+	if (received_interval > expected_interval) {
+		/* If we receive some late packets it is possible for the packets
+		 * we received in this interval to exceed the number we expected.
+		 * We update the expected so that the packet loss calculations
+		 * show that no packets are lost.
+		 */
+		expected_interval = received_interval;
+	}
 	lost_interval = expected_interval - received_interval;
 	if (expected_interval == 0 || lost_interval <= 0) {
 		*fraction_lost = 0;
@@ -6801,7 +6809,7 @@ static struct ast_frame *ast_rtp_interpret(struct ast_rtp_instance *instance, st
 			ast_log(LOG_WARNING, "scheduling RTCP transmission failed.\n");
 		}
 	}
-	if ((int)rtp->lastrxseqno - (int)seqno  > 100) /* if so it would indicate that the sender cycled; allow for misordering */
+	if ((int)prev_seqno - (int)seqno  > 100) /* if so it would indicate that the sender cycled; allow for misordering */
 		rtp->cycles += RTP_SEQ_MOD;
 
 	/* If we are directly bridged to another instance send the audio directly out,