gprs_ns2: gprs_ns2_free(): add missing talloc_free

It clean up all the space except the nsi itself.

Change-Id: Ia3fbe5d679d0af75b2b0db020f1eb082d629cf50
diff --git a/src/gb/gprs_ns2.c b/src/gb/gprs_ns2.c
index 86813f3..7a15352 100644
--- a/src/gb/gprs_ns2.c
+++ b/src/gb/gprs_ns2.c
@@ -1001,6 +1001,8 @@
 	llist_for_each_entry_safe(bind, tbind, &nsi->binding, list) {
 		gprs_ns2_free_bind(bind);
 	}
+
+	talloc_free(nsi);
 }
 
 /*! Configure whether a NS Instance should dynamically create NSEs based on incoming traffic.