shill: Fix header guards to conform to coding style.

BUG=chromium:385849
TEST=Tested the following:
1. `USE='cellular wimax' FEATURES=test emerge-$BOARD platform2`
2. `cpplint.py --filter=-build/include_order shill/*.h` reports no
   'build/header_guard' issue.

Change-Id: I1a3972a1f88e5001550eccd561633bd4e5c5faba
Reviewed-on: https://chromium-review.googlesource.com/206680
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/glib_io_ready_handler.h b/glib_io_ready_handler.h
index ffffca1..9836085 100644
--- a/glib_io_ready_handler.h
+++ b/glib_io_ready_handler.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SHILL_GLIB_IO_READY_HANDLER_
-#define SHILL_GLIB_IO_READY_HANDLER_
+#ifndef SHILL_GLIB_IO_READY_HANDLER_H_
+#define SHILL_GLIB_IO_READY_HANDLER_H_
 
 #include <stdio.h>
 #include <glib.h>
@@ -40,4 +40,4 @@
 
 }  // namespace shill
 
-#endif  // SHILL_GLIB_IO_READY_HANDLER_
+#endif  // SHILL_GLIB_IO_READY_HANDLER_H_