Use port number #defines for VTY and CTRL ports

.. as defined in libosmocore
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_ctrl.c b/openbsc/src/osmo-bsc_nat/bsc_nat_ctrl.c
index 14985e7..877a8c8 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_ctrl.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_ctrl.c
@@ -23,6 +23,7 @@
 
 #include <osmocom/ctrl/control_cmd.h>
 #include <osmocom/ctrl/control_if.h>
+#include <osmocom/ctrl/ports.h>
 
 #include <openbsc/ctrl.h>
 #include <openbsc/bsc_nat.h>
@@ -383,7 +384,7 @@
 	int rc;
 
 
-	ctrl = bsc_controlif_setup(NULL, 4250);
+	ctrl = bsc_controlif_setup(NULL, OSMO_CTRL_PORT_BSC_NAT);
 	if (!ctrl) {
 		fprintf(stderr, "Failed to initialize the control interface. Exiting.\n");
 		return NULL;