reworked MNCC codebase

This is Harald's reworked MNCC base, slowly heading towards integration
into master.  The key changes are:
* provide much more structure to the data in gsm_mncc
* encode_* and decode_* functions now take a structure rather than tons
  of individual arguments (whose order nobody can remember)
* make sure we don't have copies of the same code everywhere by introducing
  mncc_set_cause() and mncc_release_ind()
* save horizontal screen space if possible
* make sure we break lines > 80 characters
diff --git a/openbsc/include/openbsc/gsm_subscriber.h b/openbsc/include/openbsc/gsm_subscriber.h
index 780d8ed..dc4f6d7 100644
--- a/openbsc/include/openbsc/gsm_subscriber.h
+++ b/openbsc/include/openbsc/gsm_subscriber.h
@@ -12,6 +12,7 @@
 #define GSM_EXTENSION_LENGTH 128
 
 struct gsm_subscriber {
+	struct gsm_network *net;
 	long long unsigned int id;
 	char imsi[GSM_IMSI_LENGTH];
 	char tmsi[GSM_TMSI_LENGTH];