ns2: Dump frame relay state to VTY during "show ns"

When doing a "show ns", let's also dump the state of the frame
relay network, with all its links and DLCs (if any).

Change-Id: I798af3e97dc014b6e0fcde86560a1809852f7510
Related: OS#4877
diff --git a/include/osmocom/gprs/frame_relay.h b/include/osmocom/gprs/frame_relay.h
index 8ab9790..81b42a6 100644
--- a/include/osmocom/gprs/frame_relay.h
+++ b/include/osmocom/gprs/frame_relay.h
@@ -33,6 +33,7 @@
 
 struct osmo_tdef;
 struct msgb;
+struct vty;
 
 enum osmo_fr_role {
 	FR_ROLE_USER_EQUIPMENT,
@@ -132,6 +133,7 @@
 /* allocate a frame relay network */
 struct osmo_fr_network *osmo_fr_network_alloc(void *ctx);
 void osmo_fr_network_free(struct osmo_fr_network *net);
+void osmo_fr_network_dump_vty(struct vty *vty, const struct osmo_fr_network *net);
 
 /* allocate a frame relay link in a given network */
 struct osmo_fr_link *osmo_fr_link_alloc(struct osmo_fr_network *net, enum osmo_fr_role role, const char *name);