Add callback for allocated lchannels

Currently it is not possible to know for which tmsi the channel
is going to be allocated. The bsc_hack will guess.. in the future
it might be forced to ask for the tmsi after the channel has been
opened...
diff --git a/include/openbsc/gsm_data.h b/include/openbsc/gsm_data.h
index 8f21524..99634f4 100644
--- a/include/openbsc/gsm_data.h
+++ b/include/openbsc/gsm_data.h
@@ -84,6 +84,9 @@
 
 	/* local end of a call, if any */
 	struct gsm_call call;
+
+	/* temporary user data, to be removed... and merged into gsm_call */
+	void *user_data;
 };
 
 #define BTS_TRX_F_ACTIVATED	0x0001
@@ -146,6 +149,7 @@
 	struct gsm_subscriber *subscriber;
 
 	void (*update_request_accepted)(struct gsm_bts *, u_int32_t);
+	void (*channel_allocated)(struct gsm_lchan *bts, enum gsm_chreq_reason_t);
 };
 
 struct gsm_network *gsm_network_init(unsigned int num_bts, u_int16_t country_code,