bsc_api: drop unknown RR messages.

Radio Resource (RR) handling is entirely done inside the BSC. However,
the current implementation forwards unknown RR messages to the MSC.
This is not compliant to the specification.

- Remove the forwarding and drop any unknown RR message.

Change-Id: I0a4d311f6939a4fcee59129daa18da4a2ab510ae

src/libbsc/bsc_api.c

@@ -773,14 +773,10 @@ static void dispatch_dtap(struct gsm_subscriber_connection *conn,
 				api->dtap(conn, link_id, msg);
 			break;
 		default:
-			/* Normally, a MSC should never receive RR
-			 * messages, but we'd rather forward what we
-			 * don't know than drop it... */
+			/* Drop unknown RR message */
 			LOGP(DRR, LOGL_NOTICE,
-			     "BSC: Passing %s 04.08 RR message to MSC\n",
-			     gsm48_rr_msg_name(msg_type));
-			if (api->dtap)
-				api->dtap(conn, link_id, msg);
+			     "%s Dropping %s 04.08 RR message from %s\n",
+			     gsm_lchan_name(conn->lchan), gsm48_rr_msg_name(msg_type));
 		}
 		break;
 	default: