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/src/libosmo-mgcp/mgcp_osmux.c b/src/libosmo-mgcp/mgcp_osmux.c
index 281595c..26817c8 100644
--- a/src/libosmo-mgcp/mgcp_osmux.c
+++ b/src/libosmo-mgcp/mgcp_osmux.c
@@ -256,8 +256,8 @@
 		.sin_port = conn_net->end.rtp_port,
 	};
 
-	conn_bts->end.stats.octets_tx += msg->len;
-	conn_bts->end.stats.packets_tx++;
+	rate_ctr_inc(&conn_bts->rate_ctr_group->ctr[RTP_PACKETS_TX_CTR]);
+	rate_ctr_add(&conn_bts->rate_ctr_group->ctr[RTP_OCTETS_TX_CTR], msg->len);
 
 	/* Send RTP data to NET */
 	/* FIXME: Get rid of conn_bts and conn_net! */
@@ -283,8 +283,8 @@
 		.sin_port = conn_bts->end.rtp_port,
 	};
 
-	conn_net->end.stats.octets_tx += msg->len;
-	conn_net->end.stats.packets_tx++;
+	rate_ctr_inc(&conn_net->rate_ctr_group->ctr[RTP_PACKETS_TX_CTR]);
+	rate_ctr_add(&conn_net->rate_ctr_group->ctr[RTP_OCTETS_TX_CTR], msg->len);	
 
 	/* Send RTP data to BTS */
 	/* FIXME: Get rid of conn_bts and conn_net! */