src: include new file osmocom/vty/misc.h for vty_out_rate_ctr_group()

This uses the new include file for vty_out_rate_ctr_group() which
available in libosmocore.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c b/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
index 90f69ae..08a9269 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
@@ -30,6 +30,7 @@
 #include <osmocom/core/rate_ctr.h>
 #include <osmocom/core/utils.h>
 #include <osmocom/vty/logging.h>
+#include <osmocom/vty/misc.h>
 
 #include <osmocom/sccp/sccp.h>