Fix of IMMIDIATE ASSIGNMENT REJECT message

The message was corrupt at several points. They are fixed now and
successfully tested.

A default T3122 timer value of 10 is defined by default now. If set to 0,
the reject message will not be sent. Note that when using existing configs
with T3122 value set to 0.
diff --git a/openbsc/src/libcommon/gsm_data.c b/openbsc/src/libcommon/gsm_data.c
index c9f41fc..dd1d93b 100644
--- a/openbsc/src/libcommon/gsm_data.c
+++ b/openbsc/src/libcommon/gsm_data.c
@@ -97,6 +97,7 @@
 	net->T3101 = GSM_T3101_DEFAULT;
 	net->T3105 = GSM_T3105_DEFAULT;
 	net->T3113 = GSM_T3113_DEFAULT;
+	net->T3122 = GSM_T3122_DEFAULT;
 	/* FIXME: initialize all other timers! */
 
 	/* default set of handover parameters */