Add getOemNetd method to INetd.aidl

OEM could get their customized OemNetd binder by this method

Bug: 120251561
Test: built, flashed, booted
        system/netd/tests/runtests.sh pass

Change-Id: I40696573c99798cab609816675ec9070d1311b91
diff --git a/server/NetdNativeService.h b/server/NetdNativeService.h
index 518530c..86d4b73 100644
--- a/server/NetdNativeService.h
+++ b/server/NetdNativeService.h
@@ -246,6 +246,8 @@
     binder::Status registerUnsolicitedEventListener(
             const android::sp<android::net::INetdUnsolicitedEventListener>& listener) override;
 
+    binder::Status getOemNetd(android::sp<android::IBinder>* listener) override;
+
   private:
     std::vector<uid_t> intsToUids(const std::vector<int32_t>& intUids);
     Permission convertPermission(int32_t permission);