[NETD-BPF#1] Move libnetdutils to frameworks/libs/net/...

libnetdutils is referenced by netd.c and TrafficController.cpp, which
are going to be mainlined. Therefore, move libnetdutils to a common
place where both mainline module and platform code (Netd) can refer to.

Bug: 202086915
Test: build; flash; cd system/netd; atest
Ignore-AOSP-First: the netd change(same topic) would not automerge from
aosp.
No-Typo-Check: Clean code move with no other changes.
BYPASS_INCLUSIVE_LANGUAGE_REASON=Clean code move with no other changes.
Change-Id: I645bfe35f6543149c9a9f894cd4158d27a481abe

staticlibs/netd/libnetdutils/include/netdutils/Misc.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#ifndef NETUTILS_MISC_H
+#define NETUTILS_MISC_H
+
+#include <map>
+
+namespace android {
+namespace netdutils {
+
+// Lookup key in map, returing a default value if key is not found
+template <typename U, typename V>
+inline const V& findWithDefault(const std::map<U, V>& map, const U& key, const V& dflt) {
+    auto it = map.find(key);
+    return (it == map.end()) ? dflt : it->second;
+}
+
+// Movable, copiable, scoped lambda (or std::function) runner. Useful
+// for running arbitrary cleanup or logging code when exiting a scope.
+//
+// Compare to defer in golang.
+template <typename FnT>
+class Cleanup {
+  public:
+    Cleanup() = delete;
+    explicit Cleanup(FnT fn) : mFn(fn) {}
+    ~Cleanup() { if (!mReleased) mFn(); }
+
+    void release() { mReleased = true; }
+
+  private:
+    bool mReleased{false};
+    FnT mFn;
+};
+
+// Helper to make a new Cleanup. Avoids complex or impossible syntax
+// when wrapping lambdas.
+//
+// Usage:
+// auto cleanup = makeCleanup([](){ your_code_here; });
+template <typename FnT>
+Cleanup<FnT> makeCleanup(FnT fn) {
+    return Cleanup<FnT>(fn);
+}
+
+}  // namespace netdutils
+}  // namespace android
+
+#endif /* NETUTILS_MISC_H */