Add a bpf_tethering_headers lib used by the programs and JNI.

This provides a place to store common definitions that can be
used by both the programs and by JNI code in the tethering
module.

Over time much of the tethering-specific code in bpf_shared.h
could move here.

Test: m
Bug: 177884581
Change-Id: I4bf2c762d61cd5db003d59880e6bf7d107ff1a07

Tethering/Android.bp

@@ -62,7 +62,10 @@ cc_library {
         "com.android.tethering",
     ],
     min_sdk_version: "30",
-    header_libs: ["bpf_syscall_wrappers"],
+    header_libs: [
+        "bpf_syscall_wrappers",
+        "bpf_tethering_headers",
+    ],
     srcs: [
         "jni/*.cpp",
     ],

Tethering/bpf_progs/Android.bp

@@ -14,6 +14,26 @@
 // limitations under the License.
 //
 
+//
+// struct definitions shared with JNI
+//
+cc_library_headers {
+    name: "bpf_tethering_headers",
+    vendor_available: false,
+    host_supported: false,
+    export_include_dirs: ["."],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    sdk_version: "30",
+    min_sdk_version: "30",
+    apex_available: ["com.android.tethering"],
+    visibility: [
+        "//packages/modules/Connectivity/Tethering",
+    ],
+}
+
 //
 // bpf kernel programs
 //

Tethering/bpf_progs/bpf_tethering.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2021 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.
+ */
+
+#pragma once
+
+// Common definitions for BPF code in the tethering mainline module.
+// These definitions are available to:
+// - The BPF programs in Tethering/bpf_progs/
+// - JNI code that depends on the bpf_tethering_headers library.