Allow VTY-based configuration of T3105

This timer will only be forwarded to BS11 and Ericsson Abis so far,
not to Nokia and ip.access BTS yet.
diff --git a/openbsc/src/libcommon/gsm_data.c b/openbsc/src/libcommon/gsm_data.c
index 6eb39b0..a235c9d 100644
--- a/openbsc/src/libcommon/gsm_data.c
+++ b/openbsc/src/libcommon/gsm_data.c
@@ -94,6 +94,7 @@
 	net->num_bts = 0;
 	net->reject_cause = GSM48_REJECT_ROAMING_NOT_ALLOWED;
 	net->T3101 = GSM_T3101_DEFAULT;
+	net->T3105 = GSM_T3105_DEFAULT;
 	net->T3113 = GSM_T3113_DEFAULT;
 	/* FIXME: initialize all other timers! */