gprs_ns2: ensure the NSE becomes dead when FR link went down

The FR code is using force unconfigured to change the state of the NSVC
when the FR link goes down. The force unconfigured state didn't
notified the NSE when changing into this state.

Related: SYS#5533
Change-Id: I4d7bbbbce26f7cde99eebe96995c50b1e812e5bd
diff --git a/src/gb/gprs_ns2_vc_fsm.c b/src/gb/gprs_ns2_vc_fsm.c
index 4dc0536..1fcc3ad 100644
--- a/src/gb/gprs_ns2_vc_fsm.c
+++ b/src/gb/gprs_ns2_vc_fsm.c
@@ -254,7 +254,10 @@
 
 static void ns2_st_unconfigured_onenter(struct osmo_fsm_inst *fi, uint32_t old_state)
 {
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
 	stop_test_procedure(fi->priv);
+	ns2_nse_notify_unblocked(priv->nsvc, false);
 }
 
 static void ns2_st_unconfigured(struct osmo_fsm_inst *fi, uint32_t event, void *data)