db: Remove the struct gsm_network from the database layer

The database code should not know about the network. Move the
setting of the network pointer into the subscriber layer.
diff --git a/openbsc/src/libmsc/gsm_04_08.c b/openbsc/src/libmsc/gsm_04_08.c
index a299590..c41443e 100644
--- a/openbsc/src/libmsc/gsm_04_08.c
+++ b/openbsc/src/libmsc/gsm_04_08.c
@@ -474,7 +474,7 @@
 		if (!conn->subscr) {
 			conn->subscr = subscr_get_by_imsi(net, mi_string);
 			if (!conn->subscr)
-				conn->subscr = db_create_subscriber(net, mi_string);
+				conn->subscr = subscr_create_subscriber(net, mi_string);
 		}
 		if (conn->loc_operation)
 			conn->loc_operation->waiting_for_imsi = 0;
@@ -586,7 +586,7 @@
 		/* look up subscriber based on IMSI, create if not found */
 		subscr = subscr_get_by_imsi(bts->network, mi_string);
 		if (!subscr) {
-			subscr = db_create_subscriber(bts->network, mi_string);
+			subscr = subscr_create_subscriber(bts->network, mi_string);
 		}
 		break;
 	case GSM_MI_TYPE_TMSI: