stats: replace packet statistic counters with libosmocore rate counters

In struct mgcp_rtp_end one finds unsigned int counters. Those should
be replaced with libosmocore rate counters

- replace packets_rx, octets_rx, packets_tx, octets_tx and
  dropped_packets with libosmocore rate counters.

Change-Id: I47c5c9006df5044e59ddebb895e62adb849d72d5
Related: OS#2517
diff --git a/include/osmocom/mgcp/mgcp_stat.h b/include/osmocom/mgcp/mgcp_stat.h
index b6c73fa..0bde8cf 100644
--- a/include/osmocom/mgcp/mgcp_stat.h
+++ b/include/osmocom/mgcp/mgcp_stat.h
@@ -30,8 +30,7 @@
 void mgcp_format_stats(char *str, size_t str_len,  struct mgcp_conn *conn);
 
 /* Exposed for test purposes only, do not use actively */
-void calc_loss(struct mgcp_rtp_state *s, struct mgcp_rtp_end *,
-			uint32_t *expected, int *loss);
+void calc_loss(struct mgcp_conn_rtp *conn, uint32_t *expected, int *loss);
 
 /* Exposed for test purposes only, do not use actively */
 uint32_t calc_jitter(struct mgcp_rtp_state *);