[RBS2000] Enable TRAU frame handling/muxing similar to BS11

Based on original patch by Gus Bourg <gus@bourg.net>
diff --git a/openbsc/src/libmsc/gsm_04_08.c b/openbsc/src/libmsc/gsm_04_08.c
index 2b61aa9..42652e2 100644
--- a/openbsc/src/libmsc/gsm_04_08.c
+++ b/openbsc/src/libmsc/gsm_04_08.c
@@ -1633,6 +1633,7 @@
 		}
 		break;
 	case GSM_BTS_TYPE_BS11:
+	case GSM_BTS_TYPE_RBS2000:
 		trau_mux_map_lchan(lchan, remote_lchan);
 		break;
 	default:
@@ -1702,6 +1703,7 @@
 				net, 0);
 		break;
 	case GSM_BTS_TYPE_BS11:
+	case GSM_BTS_TYPE_RBS2000:
 		if (enable)
 			return trau_recv_lchan(lchan, callref);
 		return trau_mux_unmap(NULL, callref);
@@ -2986,6 +2988,7 @@
 			}
 			return rtp_send_frame(trans->conn->lchan->abis_ip.rtp_socket, arg);
 		case GSM_BTS_TYPE_BS11:
+		case GSM_BTS_TYPE_RBS2000:
 			return trau_send_frame(trans->conn->lchan, arg);
 		default:
 			DEBUGP(DCC, "Unknown BTS type %u\n", bts->type);