Write configuration correctly from vty (alert notifications)

The default is [yes] alert-notifications, therefore write
"no alert-notifications" in the case that this has
been set, in order to preserve configuration after
write is called from vty.

Change-Id: I079aea96ee83fbf04f782dcab344d41a4ef04657
diff --git a/src/libmsc/smpp_vty.c b/src/libmsc/smpp_vty.c
index 4c179d4..9026f6c 100644
--- a/src/libmsc/smpp_vty.c
+++ b/src/libmsc/smpp_vty.c
@@ -582,8 +582,8 @@
 		vty_out(vty, "  osmocom-extensions%s", VTY_NEWLINE);
 	if (acl->dcs_transparent)
 		vty_out(vty, "  dcs-transparent%s", VTY_NEWLINE);
-	if (acl->alert_notifications)
-		vty_out(vty, "  alert-notifications%s", VTY_NEWLINE);
+	if (!acl->alert_notifications)
+		vty_out(vty, "  no alert-notifications%s", VTY_NEWLINE);
 
 	llist_for_each_entry(r, &acl->route_list, list)
 		write_esme_route_single(vty, r);