shill: WiFi: Set disable_vht parameter

Provide a run-time Manager property which sets the WiFi
provider's "disable_vht" field.  This will be used to enable or
disable VHT in wpa_supplicant.

CQ-DEPEND=CL:189960,CL:189941
BUG=chromium:352260
TEST=Unit tests

Change-Id: Id380ce15982418dea2845f722460c612aee565db
Reviewed-on: https://chromium-review.googlesource.com/189961
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
diff --git a/manager.h b/manager.h
index da6dcfa..b426289 100644
--- a/manager.h
+++ b/manager.h
@@ -447,6 +447,8 @@
                           Technology::Identifier tech) const;
   bool IsDefaultProfile(StoreInterface *storage);
   void EmitDeviceProperties();
+  bool SetDisableWiFiVHT(const bool &disable_wifi_vht, Error *error);
+  bool GetDisableWiFiVHT(Error *error);
 
   // Unload a service while iterating through |services_|.  Returns true if
   // service was erased (which means the caller loop should not increment
@@ -473,6 +475,10 @@
   void HelpRegisterConstDerivedStrings(
       const std::string &name,
       Strings(Manager::*get)(Error *));
+  void HelpRegisterDerivedBool(
+      const std::string &name,
+      bool(Manager::*get)(Error *error),
+      bool(Manager::*set)(const bool &value, Error *error));
 
   bool HasProfile(const Profile::Identifier &ident);
   void PushProfileInternal(const Profile::Identifier &ident,