abis_nm: Create a signal data structure for the NACK message

Provide the message type and the msgb of the NACK message.
diff --git a/openbsc/include/openbsc/signal.h b/openbsc/include/openbsc/signal.h
index 0738f80..e614ee5 100644
--- a/openbsc/include/openbsc/signal.h
+++ b/openbsc/include/openbsc/signal.h
@@ -1,5 +1,5 @@
 /* Generic signalling/notification infrastructure */
-/* (C) 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
+/* (C) 2009-2010 by Holger Hans Peter Freyther <zecke@selfish.org>
  * (C) 2009 by Harald Welte <laforge@gnumonks.org>
  * All Rights Reserved
  *
@@ -139,6 +139,11 @@
 	u_int8_t msg_type;	
 };
 
+struct nm_nack_signal_data {
+	struct msgb *msg;
+	uint8_t mt;
+};
+
 struct challoc_signal_data {
 	struct gsm_bts *bts;
 	struct gsm_lchan *lchan;