mgcp: Calculate the packet loss as of Appendix A of RFC 3550

Calculate the expected packages and packet loss as of RFC 3550.
The values should be clamped but our packet loss counter is 32
bits and not 24 and we should clamp at other values but I am
waiting for some issues first before dealing with that.
diff --git a/openbsc/src/libmgcp/mgcp_protocol.c b/openbsc/src/libmgcp/mgcp_protocol.c
index d57ad00..0d8e9ea 100644
--- a/openbsc/src/libmgcp/mgcp_protocol.c
+++ b/openbsc/src/libmgcp/mgcp_protocol.c
@@ -1121,8 +1121,14 @@
 
 void mgcp_format_stats(struct mgcp_endpoint *endp, char *msg, size_t size)
 {
-	snprintf(msg, size, "\r\nP: PS=%u, OS=%u, PR=%u, OR=%u",
+	uint32_t expected;
+	int ploss;
+	mgcp_state_calc_loss(&endp->net_state, &endp->net_end,
+				&expected, &ploss);
+
+	snprintf(msg, size, "\r\nP: PS=%u, OS=%u, PR=%u, OR=%u, PL=%d",
 			endp->bts_end.packets, endp->bts_end.octets,
-			endp->net_end.packets, endp->net_end.octets);
+			endp->net_end.packets, endp->net_end.octets,
+			ploss);
 	msg[size - 1] = '\0';
 }