ns: TC_sns_bss_change_weight_timeout rework TC to use g_handle_rx_alive

With g_handle_rx_alive the test case doesn't need to use alt{}
as f_ns_exp takes care of the NS_ALIVE.

Related: OS#5036
Change-Id: I45f4392b556912bf60859f354a5687a44e6beeb1
diff --git a/ns/NS_Tests.ttcn b/ns/NS_Tests.ttcn
index 29e5669..f69bbe0 100644
--- a/ns/NS_Tests.ttcn
+++ b/ns/NS_Tests.ttcn
@@ -469,6 +469,7 @@
 }
 
 testcase TC_sns_bss_change_weight() runs on RAW_Test_CT {
+	g_handle_rx_alive := true;
 	f_init_vty();
 	f_init_ns_codec(mp_nsconfig);
 	f_incoming_sns_size();
@@ -487,6 +488,7 @@
 	var template PDU_NS rx;
 	var NSVCConfiguration nsvc_cfg;
 
+	g_handle_rx_alive := true;
 	f_init_vty();
 	f_init_ns_codec(mp_nsconfig);
 	f_incoming_sns_size();
@@ -507,14 +509,8 @@
 		rx := tr_SNS_CHG_WEIGHT(g_nsconfig.nsei, ?, v4 := omit, v6 := v6_elem);
 	}
 
-	alt {
-	[] NSCP[0].receive(rx) {
-		i := i + 1;
-		if (i < 3) {
-			repeat;
-		}
-	}
-	[] as_rx_alive_tx_ack();
+	for (i := 0; i < 3; i := i + 1) {
+		f_ns_exp(rx);
 	}
 
 	if (nsvc_cfg.provider.ip.address_family == AF_INET) {