Explicitly select "HT40-" for 5GHz HT40 tests

server/site_tests/network_WiFiMatFunc/040CheckSGI40

 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 { "name":"CheckSGI40",
   "skip_test":"Needs a kernel enhancement",
   "steps":[             # Channel 48
     [ "create",         { "type":"hostap" } ],
-    [ "config",         { "channel":"5240", "ht40":None, "puren":None,
+    [ "config",         { "channel":"5240", "ht40-":None, "puren":None,
                           "shortgi":None } ],
     [ "connect",        { "security":"none" } ],
     [ "client_check_shortgi40", [ "true" ] ],
     [ "server_netperf", { "test":"TCP_STREAM" } ],
     # verify SGI stats
     [ "destroy" ],
   ],
 }