[NETD-BPF#19] Mainline part of bpf code from netd

1. Add libnetd_updatable.so in com.android.tethering. The library is
loaded by netd. Currently, it mainly targets on a few functions which
access BPF maps. The functionality may extend in the future.

2. Attach gcroup progs from libnetd_updatable.so.

3. Move (privileged)TagSocket and untagSocket implementation to mainline
module. Combine privilegedTagSocket and untagSocket into a single
function.

4. Split related unit tests from netd_unit_test to
libnetd_updatable_unit_test as well.

Bug: 202086915
Test: cd system/netd; atest
Test: atest TrafficStatsTest NetworkUsageStatsTest

Change-Id: Ib556458103a4cbb643c1342d9b689ac692160de0
diff --git a/netd/libnetd_updatable.map.txt b/netd/libnetd_updatable.map.txt
new file mode 100644
index 0000000..dcb11a1
--- /dev/null
+++ b/netd/libnetd_updatable.map.txt
@@ -0,0 +1,27 @@
+#
+# 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.
+#
+
+# This lists the entry points visible to applications that use the libnetd_updatable
+# library. Other entry points present in the library won't be usable.
+
+LIBNETD_UPDATABLE {
+  global:
+    libnetd_updatable_init; # apex
+    libnetd_updatable_tagSocket; # apex
+    libnetd_updatable_untagSocket; # apex
+  local:
+    *;
+};