Introduce Netd APIs for multinetworks.

Just stubs for now. Implementation will follow in subsequent CLs.

Change-Id: I10a2e4aca594c10a26d58afb4c250141386d3f0f
(cherry picked from commit 0d5146bed37b4e5b6909617e5f958a66bfee1e48)
diff --git a/NetId.cpp b/NetId.cpp
new file mode 100644
index 0000000..a07cc9f
--- /dev/null
+++ b/NetId.cpp
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#include "NetId.h"
+
+bool isNetIdValid(unsigned int netId) {
+    return MIN_NET_ID <= netId && netId <= MAX_NET_ID;
+}