library: add a receive equivalent for ts_RSL_ChanMode_SIGN

Also take a chance to enrich the already existing send template.

Change-Id: Id39ca75a9194d7c62b9e5e2d96e766c4940c8281
Related: OS#1572, OS#4396
diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index 8fc0fa9..a0d2cfe 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -7921,7 +7921,7 @@
 	var ConnHdlrPars pars;
 	pars.t_guard := 60.0;
 	f_init();
-	ch_mode := ts_RSL_ChanMode_SIGN(dtx_downlink := dtxd);
+	ch_mode := ts_RSL_ChanMode_SIGN(dtxd := dtxd);
 	for (var integer i := 0; i < sizeof(g_AllChannels); i := i + 1) {
 		pars := valueof(t_Pars(g_AllChannels[i], ch_mode));
 		if (dtxd) {