nat: Switch per BSC counters to the rate ctr.

This is switching the simple statistics to the rate counter
and is updating all users...
diff --git a/openbsc/src/nat/bsc_nat_vty.c b/openbsc/src/nat/bsc_nat_vty.c
index eea5dd8..c09eca4 100644
--- a/openbsc/src/nat/bsc_nat_vty.c
+++ b/openbsc/src/nat/bsc_nat_vty.c
@@ -27,6 +27,7 @@
 #include <openbsc/vty.h>
 
 #include <osmocore/talloc.h>
+#include <osmocore/rate_ctr.h>
 
 #include <sccp/sccp.h>
 
@@ -196,11 +197,7 @@
 
 		vty_out(vty, " BSC lac: %d nr: %d%s",
 			conf->lac, conf->nr, VTY_NEWLINE);
-		vty_out(vty, "   SCCP Connnections %lu total, %lu calls%s",
-			counter_get(conf->stats.sccp.conn),
-			counter_get(conf->stats.sccp.calls), VTY_NEWLINE);
-		vty_out(vty, "   BSC Connections %lu total%s",
-			counter_get(conf->stats.net.reconn), VTY_NEWLINE);
+		vty_out_rate_ctr_group(vty, " ", conf->stats.ctrg);
 	}
 
 	return CMD_SUCCESS;