ports.h: Add VTY port for GGSN

Change-Id: I5bd49fbc19e88db96b4adbd56c82e7936059551c
diff --git a/include/osmocom/vty/ports.h b/include/osmocom/vty/ports.h
index 8f8ef75..ab3e1d5 100644
--- a/include/osmocom/vty/ports.h
+++ b/include/osmocom/vty/ports.h
@@ -26,4 +26,6 @@
 #define OSMO_VTY_PORT_MNCC_SIP	4256
 /* 4257 used by control interface */
 #define OSMO_VTY_PORT_HLR	4258
+/* 4259 used by control interface */
+#define OSMO_VTY_PORT_GGSN	4260
 /* When adding/changing port numbers, keep docs and wiki in sync. See above. */