shill: enable background scanning for wifi

When connecting to a WiFi service, supply wpa_supplicant with background
scan configuration parameters. Also, allow bgscan parameters to be
configured via RPC.

Collateral change: added NOTIMPLEMENTED log messages for ClearProperty
methods on {Device,IPConfig,Service}DBusAdaptor

BUG=chromium-os:24309
TEST=unit tests, WiFiRoaming.003SSIDMultiSwitchBack

Change-Id: I3289684bcae58a01be61d2341fd6a1099c1c7f6f
Reviewed-on: https://gerrit.chromium.org/gerrit/13844
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: mukesh agrawal <quiche@chromium.org>
diff --git a/ipconfig_dbus_adaptor.cc b/ipconfig_dbus_adaptor.cc
index e409684..912c42d 100644
--- a/ipconfig_dbus_adaptor.cc
+++ b/ipconfig_dbus_adaptor.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -77,8 +77,12 @@
   }
 }
 
-void IPConfigDBusAdaptor::ClearProperty(const std::string& /*name*/,
+void IPConfigDBusAdaptor::ClearProperty(const std::string &name,
                                         ::DBus::Error &/*error*/) {
+  NOTIMPLEMENTED() << " Ignoring request to clear " << name
+                   << " property of IPConfig " << ipconfig_->serial()
+                   << " (associated with Device " << ipconfig_->device_name()
+                   << ")";
 }
 
 void IPConfigDBusAdaptor::Remove(::DBus::Error &/*error*/) {