SIP_Templates: tr_SIP_REGISTER(): Pass via field directly as a param

Similar to other templates which already required it.
There's no user of this template (yet).

Change-Id: I9fe477370e028543b04dee35a3285ddae6bb2c59
diff --git a/library/SIP_Templates.ttcn b/library/SIP_Templates.ttcn
index e115bb7..3492dc4 100644
--- a/library/SIP_Templates.ttcn
+++ b/library/SIP_Templates.ttcn
@@ -572,14 +572,14 @@
 		template (present) CallidString call_id := ?,
 		template (present) SipAddr from_addr := ?,
 		template (present) SipAddr to_addr := ?,
+		template (present) Via via := tr_Via_from(f_tr_HostPort_opt_defport(?)),
 		template integer seq_nr := *,
 		template Contact contact := *,
 		template Expires expires := *,
 		template charstring body := *) := {
 	requestLine := tr_SIP_ReqLine(REGISTER_E, sip_url_host_port),
 	msgHeader := tr_SIP_msgh_std(call_id, from_addr, to_addr, contact,
-				     tr_Via_from(f_tr_HostPort_opt_defport(from_addr.addr.nameAddr.addrSpec.hostPort)),
-				     "REGISTER", *, seq_nr,
+				     via, "REGISTER", *, seq_nr,
 				     expires := expires),
 	messageBody := body,
 	payload := omit