bs11: make bs11_config build again

The BS-11 related tool bs11_config is currently not built due
to dependancy issues added by GSCON FSM.

- Re-Add bs11_config to makefile.am
- Add dependencies and stubs

Change-Id: I77ee8d2d36813ad98542317d003a9057c4f84e75
Related: OS#2823
diff --git a/src/utils/bs11_config.c b/src/utils/bs11_config.c
index bc0f488..e7c8336 100644
--- a/src/utils/bs11_config.c
+++ b/src/utils/bs11_config.c
@@ -969,3 +969,15 @@
 
 	exit(0);
 }
+
+/* Stub */
+int osmo_bsc_sigtran_send(struct gsm_subscriber_connection *conn, struct msgb *msg)
+{
+	return 0;
+}
+
+/* Stub */
+int osmo_bsc_sigtran_open_conn(struct gsm_subscriber_connection *conn, struct msgb *msg)
+{
+	return 0;
+}