shill: add disconnect reason to log messages

Allow logging of function/reason for triggering disconnect.

BUG=chromium:227295
TEST=unit tests

Change-Id: I92ea3cca664c060bc02bbb8d50d303ce11d1a7de
Reviewed-on: https://chromium-review.googlesource.com/207020
Tested-by: Samuel Tan <samueltan@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Queue: Samuel Tan <samueltan@chromium.org>
diff --git a/mock_cellular.h b/mock_cellular.h
index a29358f..e6430be 100644
--- a/mock_cellular.h
+++ b/mock_cellular.h
@@ -28,7 +28,7 @@
   virtual ~MockCellular();
 
   MOCK_METHOD1(Connect, void(Error *error));
-  MOCK_METHOD1(Disconnect, void(Error *error));
+  MOCK_METHOD2(Disconnect, void(Error *error, const char *reason));
   MOCK_METHOD3(OnDBusPropertiesChanged, void(
       const std::string &interface,
       const DBusPropertiesMap &changed_properties,