Add missing arpa/inet.h include for ntohl.

Clang build fix. Not sure why this is happening with gcc.

Change-Id: Ic3e192e31ba8d1d78dab83a6af13e82d261e5938
diff --git a/gatekeeperd/tests/gatekeeper_test.cpp b/gatekeeperd/tests/gatekeeper_test.cpp
index 15b2b69..47a8bfa 100644
--- a/gatekeeperd/tests/gatekeeper_test.cpp
+++ b/gatekeeperd/tests/gatekeeper_test.cpp
@@ -14,11 +14,12 @@
  * limitations under the License.
  */
 
-#include <gtest/gtest.h>
-#include <UniquePtr.h>
+#include <arpa/inet.h>
 #include <iostream>
 
+#include <gtest/gtest.h>
 #include <hardware/hw_auth_token.h>
+#include <UniquePtr.h>
 
 #include "../SoftGateKeeper.h"