bsc_api: Add stub for the cipher mode command.
diff --git a/openbsc/src/bsc_api.c b/openbsc/src/bsc_api.c
index e5c9e9c..44ec420 100644
--- a/openbsc/src/bsc_api.c
+++ b/openbsc/src/bsc_api.c
@@ -132,6 +132,12 @@
 	return 0;
 }
 
+int gsm0808_cipher_mode(struct gsm_subscriber_connection *conn, int cipher,
+			uint8_t *key, int len)
+{
+	return -1;
+}
+
 int gsm0808_clear(struct gsm_subscriber_connection* conn)
 {
 	struct gsm_lchan *lchan;