sms: Make default SMS validity period configurable via VTY

Change-Id: Ie2c81c1d5795dd9aaf07b9766013f20b01abc762
diff --git a/tests/test_nodes.vty b/tests/test_nodes.vty
index ac3ff16..cb617fc 100644
--- a/tests/test_nodes.vty
+++ b/tests/test_nodes.vty
@@ -183,6 +183,7 @@
  queue max-failure 1
  database delete-delivered 1
  database delete-expired 1
+ validity-period default 10080
 end
 
 OsmoMSC# configure terminal