Move BPF offload program from netd to mainline

Test: as the follows.
$ adb shell ls sys/fs/bpf | grep offload
map_offload_tether_ingress_map
map_offload_tether_limit_map
map_offload_tether_stats_map
prog_offload_schedcls_ingress_tether_ether
prog_offload_schedcls_ingress_tether_rawip

$ adb shell dumpsys netd --short
  TetherController
    BPF ingress map: iif(iface) v6addr -> oif(iface) srcmac ..
      13(rmnet_data3) 2401:e180:8842:6e3:bc6a:2e45:c30:f418 -> ..
    BPF stats (downlink): iif(iface) -> packets bytes errors
      13(rmnet_data3) -> 7 488 0
    BPF limit: iif(iface) -> bytes
      13(rmnet_data3) -> 9223372036854775807

Log:
bpfloader: Loaded object: /apex/com.android.tethering/etc/bpf/offload.o

Change-Id: I71b7efb1f4bd6eb1cd469a0e1e4a56342dc6e579
diff --git a/Tethering/bpf_progs/Android.bp b/Tethering/bpf_progs/Android.bp
new file mode 100644
index 0000000..d54f861
--- /dev/null
+++ b/Tethering/bpf_progs/Android.bp
@@ -0,0 +1,33 @@
+//
+// Copyright (C) 2020 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.
+//
+
+//
+// bpf kernel programs
+//
+bpf {
+    name: "offload.o",
+    srcs: ["offload.c"],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    include_dirs: [
+        // TODO: get rid of system/netd.
+        "system/netd/bpf_progs",             // for bpf_net_helpers.h
+        "system/netd/libnetdbpf/include",    // for bpf_shared.h
+        "system/netd/libnetdutils/include",  // for UidConstants.h
+    ],
+}