shill: Sort headers alphabetically (build/include_alpha)

We are going to enable build/include_alpha linter warning soon,
so in preparation for this, fixed the warnings in shill.

BUG=None
TEST=cpplint.py --filter=-build/include_order,+build/include_alpha shill/*

Change-Id: I113ed7f9dd3f465a3f660599320cdb434e7cc214
Reviewed-on: https://chromium-review.googlesource.com/209636
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/connection_health_checker.h b/connection_health_checker.h
index 7e2e9a8..0ca2685 100644
--- a/connection_health_checker.h
+++ b/connection_health_checker.h
@@ -17,8 +17,8 @@
 #include <gtest/gtest_prod.h>
 
 #include "shill/refptr_types.h"
-#include "shill/sockets.h"
 #include "shill/socket_info.h"
+#include "shill/sockets.h"
 
 namespace shill {