mscsplit: add gsm_network backpointer to gsm_subscriber_connection

We want to be able to use a network backpointer without having to go through a
gsm_bts struct.

This commit adds the network pointer, the subsequent commit applies direct
access to the network structure from gsm_subscriber_connection.

Change-Id: If8870972f1b3e333c2a4cce97cdc95bdee0382a1
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 26efeaa..ffb7dd2 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -134,6 +134,8 @@
 	struct osmo_bsc_sccp_con *sccp_con;
 
 	/* back pointers */
+	struct gsm_network *network;
+
 	int in_release;
 	struct gsm_lchan *lchan;
 	struct gsm_lchan *ho_lchan;
diff --git a/openbsc/src/libbsc/bsc_api.c b/openbsc/src/libbsc/bsc_api.c
index f42598a..02751f4 100644
--- a/openbsc/src/libbsc/bsc_api.c
+++ b/openbsc/src/libbsc/bsc_api.c
@@ -247,6 +247,7 @@
 	if (!conn)
 		return NULL;
 
+	conn->network = net;
 	conn->lchan = lchan;
 	conn->bts = lchan->ts->trx->bts;
 	lchan->conn = conn;