Assign default values for T3101 and T3113

Without those default values, old config files will no longer work
after commit 23975e718fd456ff8be7effbb915903f1bc173be
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index 8212346..88de4c4 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -198,6 +198,9 @@
 	net->country_code = country_code;
 	net->network_code = network_code;
 	net->num_bts = 0;
+	net->T3101 = GSM_T3101_DEFAULT;
+	net->T3113 = GSM_T3113_DEFAULT;
+	/* FIXME: initialize all other timers! */
 
 	INIT_LLIST_HEAD(&net->trans_list);
 	INIT_LLIST_HEAD(&net->upqueue);