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
(cherry picked from commit d97a30863794172ec5e6fa0bc16d72fb937d66eb)
Merged-In: I9859ff3df608c058786b4e2b91cb6cd5f38e653a
diff --git a/tetheroffload/aidl/Android.bp b/tetheroffload/aidl/Android.bp
new file mode 100644
index 0000000..1d80586
--- /dev/null
+++ b/tetheroffload/aidl/Android.bp
@@ -0,0 +1,27 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+aidl_interface {
+    name: "android.hardware.tetheroffload",
+    vendor_available: true,
+    srcs: ["android/hardware/tetheroffload/*.aidl"],
+    stability: "vintf",
+    backend: {
+        cpp: {
+            enabled: false,
+        },
+        java: {
+            sdk_version: "module_current",
+            apex_available: [
+                "com.android.tethering",
+            ],
+            min_sdk_version: "30",
+            enabled: true,
+        },
+        ndk: {
+            apps_enabled: false,
+        },
+    },
+    frozen: false,
+}