Convert Tetheroffload HIDL to AIDL.

This patch converts Tetheroffload HIDL to AIDL and adds an empty
example implementation.
There are some changes in AIDL HAL:
1. Combine IOffloadConfig and IOffloadControl into IOffload
2. Use AIDL builtin errors exception code with message as return

Bug: b/205762647
Test: m android.hardware.tetheroffload-update-api
      m android.hardware.tetheroffload-V1-ndk
      m android.hardware.tetheroffload-service.example
      atest VtsHalTetheroffloadTargetTest
Change-Id: I9859ff3df608c058786b4e2b91cb6cd5f38e653a
diff --git a/tetheroffload/aidl/default/main.cpp b/tetheroffload/aidl/default/main.cpp
new file mode 100644
index 0000000..6633630
--- /dev/null
+++ b/tetheroffload/aidl/default/main.cpp
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Offload.h"
+
+#include <android-base/logging.h>
+#include <android/binder_manager.h>
+#include <android/binder_process.h>
+
+using aidl::android::hardware::tetheroffload::impl::example::Offload;
+
+int main() {
+    ABinderProcess_setThreadPoolMaxThreadCount(0);
+    std::shared_ptr<Offload> offload = ndk::SharedRefBase::make<Offload>();
+
+    binder_status_t status = AServiceManager_addService(
+            offload->asBinder().get(), Offload::makeServiceName("default").c_str());
+    CHECK_EQ(status, STATUS_OK);
+
+    ABinderProcess_joinThreadPool();
+    return EXIT_FAILURE;  // should not reach
+}