apmanager: add support for HT capability

Parse wiphy's HT capability and add it to the AP service's configuration
file to correctly support AP in 80211n mode.

BUG=chromium:431763
TEST=unittests and manual test by using python to invoke dbus calls
     to start AP service in 802.11n mode.

Change-Id: I6c902136832eea6b38b806f733231d6cbe14e3f6
Reviewed-on: https://chromium-review.googlesource.com/231681
Reviewed-by: Peter Qiu <zqiu@chromium.org>
Commit-Queue: Peter Qiu <zqiu@chromium.org>
Tested-by: Peter Qiu <zqiu@chromium.org>
diff --git a/manager.h b/manager.h
index a22f71c..4b8a1fd 100644
--- a/manager.h
+++ b/manager.h
@@ -45,7 +45,11 @@
 
   virtual void RegisterDevice(scoped_refptr<Device> device);
 
+  // Return an unuse device with AP interface mode support.
   virtual scoped_refptr<Device> GetAvailableDevice();
+
+  // Return the device that's associated with the given interface
+  // |interface_name|.
   virtual scoped_refptr<Device> GetDeviceFromInterfaceName(
       const std::string& interface_name);