MSC_ConnHdlr: Fix f_rsl_reply() for RSL_MT_ENCR_CMD

In all RSL messages the link identifier is usually the second IE.
However, as the only known exception, the RSL Encryption Command has it
as third IE.

Fixes the following error message:
Dynamic test case error: Using non-selected field link_id in a value of
union type @RSL_Types.RSL_IE_Body

Change-Id: I2bbb83b5394d0b693a47d286beed5c699ab6e8ae
diff --git a/bsc/MSC_ConnectionHandler.ttcn b/bsc/MSC_ConnectionHandler.ttcn
index a76d1d6..028f1b4 100644
--- a/bsc/MSC_ConnectionHandler.ttcn
+++ b/bsc/MSC_ConnectionHandler.ttcn
@@ -96,6 +96,11 @@
 function f_rsl_reply(template PDU_ML3_MS_NW l3, RSL_Message orig) runs on MSC_ConnHdlr {
 	var RslChannelNr chan_nr := orig.ies[0].body.chan_nr;
 	var RslLinkId link_id := orig.ies[1].body.link_id;
+	if (orig.msg_type == RSL_MT_ENCR_CMD) {
+		link_id := orig.ies[2].body.link_id;
+	} else {
+		link_id := orig.ies[1].body.link_id;
+	}
 	RSL.send(ts_RSL_DATA_IND(chan_nr, link_id, enc_PDU_ML3_MS_NW(valueof(l3))));
 }