mgcp_conn: rename field s/rate_ctr_group/ctrg/g

This makes all lines operating on rate groups way shorter. The "ctrg"
naming is already used in tons of places in osmocom code.

Change-Id: I745eddbf66e7d811bb73c8ae9bb54ea93073c71b
diff --git a/src/libosmo-mgcp/mgcp_vty.c b/src/libosmo-mgcp/mgcp_vty.c
index f6c3c75..6183867 100644
--- a/src/libosmo-mgcp/mgcp_vty.c
+++ b/src/libosmo-mgcp/mgcp_vty.c
@@ -169,11 +169,11 @@
 	struct rate_ctr *rx_packets, *rx_bytes;
 	struct rate_ctr *dropped_packets;
 
-	tx_packets = rate_ctr_group_get_ctr(conn->rate_ctr_group, RTP_PACKETS_TX_CTR);
-	tx_bytes = rate_ctr_group_get_ctr(conn->rate_ctr_group, RTP_OCTETS_TX_CTR);
-	rx_packets = rate_ctr_group_get_ctr(conn->rate_ctr_group, RTP_PACKETS_RX_CTR);
-	rx_bytes = rate_ctr_group_get_ctr(conn->rate_ctr_group, RTP_OCTETS_RX_CTR);
-	dropped_packets = rate_ctr_group_get_ctr(conn->rate_ctr_group, RTP_DROPPED_PACKETS_CTR);
+	tx_packets = rate_ctr_group_get_ctr(conn->ctrg, RTP_PACKETS_TX_CTR);
+	tx_bytes = rate_ctr_group_get_ctr(conn->ctrg, RTP_OCTETS_TX_CTR);
+	rx_packets = rate_ctr_group_get_ctr(conn->ctrg, RTP_PACKETS_RX_CTR);
+	rx_bytes = rate_ctr_group_get_ctr(conn->ctrg, RTP_OCTETS_RX_CTR);
+	dropped_packets = rate_ctr_group_get_ctr(conn->ctrg, RTP_DROPPED_PACKETS_CTR);
 
 	vty_out(vty,
 		"   Packets Sent: %" PRIu64 " (%" PRIu64 " bytes total)%s"