Test for races in IptablesRestoreController::Init.

Bug: 28362720
Test: angler builds, boots
Test: netd_{unit,integration}_test pass
Change-Id: I73ed28c7e7edaeb65a3b346b89ec69f472fd5974
diff --git a/server/IptablesRestoreController.h b/server/IptablesRestoreController.h
index 6850d0d..b1c8dcd 100644
--- a/server/IptablesRestoreController.h
+++ b/server/IptablesRestoreController.h
@@ -68,6 +68,8 @@
     // |POLL_TIMEOUT_MS * MAX_RETRIES|. Chosen so that the overall timeout is 1s.
     static int POLL_TIMEOUT_MS;
 
+    void Init();
+
 private:
     static IptablesProcess* forkAndExec(const IptablesProcessType type);