isup: Make it possible for the STP to handle/not  handle ISUP messages

Add an option to decide if we should handle GROUP BLOCK and RESET
messages inside the STP or if we should forward those as well.
diff --git a/include/bsc_data.h b/include/bsc_data.h
index 698a33f..fe6d295 100644
--- a/include/bsc_data.h
+++ b/include/bsc_data.h
@@ -124,6 +124,9 @@
 	int ni_ni;
 	int ni_spare;
 
+	/* isup handling */
+	int isup_pass;
+
 	/* LAC of the cell */
 	struct gsm48_loc_area_id lai;
 	uint16_t mcc;