Fix cannot create Nat-T keepalive on mobile data

Currently phone process fail to unparcel NattKeepalivePacketData
since it is not in framework. Moves NattKeepalivePacketData to
framework to make it can be utilized by telephony.

This change also removes the error feedback triggered by calling
add keepalive packet filter to an unsupported network agent. This
is misinterpreted by KeepaliveTracker that start keepalive is
failing.

Bug: 134048171
Test: 1. atest android.net.cts.ConnectivityManagerTest#testSocketKeepaliveLimitTelephony
      2. atest android.net.cts.ConnectivityManagerTest
      3. atest FrameworksNetTests
      4. atest FrameworksTelephonyTests
Change-Id: If630d5b339aa722717258c721daa8ead8c431e2d
diff --git a/core/java/android/net/NattKeepalivePacketData.java b/core/java/android/net/NattKeepalivePacketData.java
new file mode 100644
index 0000000..a77c244
--- /dev/null
+++ b/core/java/android/net/NattKeepalivePacketData.java
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+package android.net;
+
+import static android.net.SocketKeepalive.ERROR_INVALID_IP_ADDRESS;
+import static android.net.SocketKeepalive.ERROR_INVALID_PORT;
+
+import android.net.SocketKeepalive.InvalidPacketException;
+import android.net.util.IpUtils;
+import android.os.Parcel;
+import android.os.Parcelable;
+import android.system.OsConstants;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/** @hide */
+public final class NattKeepalivePacketData extends KeepalivePacketData implements Parcelable {
+    // This should only be constructed via static factory methods, such as
+    // nattKeepalivePacket
+    private NattKeepalivePacketData(InetAddress srcAddress, int srcPort,
+            InetAddress dstAddress, int dstPort, byte[] data) throws
+            InvalidPacketException {
+        super(srcAddress, srcPort, dstAddress, dstPort, data);
+    }
+
+    /**
+     * Factory method to create Nat-T keepalive packet structure.
+     */
+    public static NattKeepalivePacketData nattKeepalivePacket(
+            InetAddress srcAddress, int srcPort, InetAddress dstAddress, int dstPort)
+            throws InvalidPacketException {
+
+        if (!(srcAddress instanceof Inet4Address) || !(dstAddress instanceof Inet4Address)) {
+            throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
+        }
+
+        if (dstPort != NattSocketKeepalive.NATT_PORT) {
+            throw new InvalidPacketException(ERROR_INVALID_PORT);
+        }
+
+        int length = IPV4_HEADER_LENGTH + UDP_HEADER_LENGTH + 1;
+        ByteBuffer buf = ByteBuffer.allocate(length);
+        buf.order(ByteOrder.BIG_ENDIAN);
+        buf.putShort((short) 0x4500);             // IP version and TOS
+        buf.putShort((short) length);
+        buf.putInt(0);                            // ID, flags, offset
+        buf.put((byte) 64);                       // TTL
+        buf.put((byte) OsConstants.IPPROTO_UDP);
+        int ipChecksumOffset = buf.position();
+        buf.putShort((short) 0);                  // IP checksum
+        buf.put(srcAddress.getAddress());
+        buf.put(dstAddress.getAddress());
+        buf.putShort((short) srcPort);
+        buf.putShort((short) dstPort);
+        buf.putShort((short) (length - 20));      // UDP length
+        int udpChecksumOffset = buf.position();
+        buf.putShort((short) 0);                  // UDP checksum
+        buf.put((byte) 0xff);                     // NAT-T keepalive
+        buf.putShort(ipChecksumOffset, IpUtils.ipChecksum(buf, 0));
+        buf.putShort(udpChecksumOffset, IpUtils.udpChecksum(buf, 0, IPV4_HEADER_LENGTH));
+
+        return new NattKeepalivePacketData(srcAddress, srcPort, dstAddress, dstPort, buf.array());
+    }
+
+    /** Parcelable Implementation */
+    public int describeContents() {
+        return 0;
+    }
+
+    /** Write to parcel */
+    public void writeToParcel(Parcel out, int flags) {
+        out.writeString(srcAddress.getHostAddress());
+        out.writeString(dstAddress.getHostAddress());
+        out.writeInt(srcPort);
+        out.writeInt(dstPort);
+    }
+
+    /** Parcelable Creator */
+    public static final Parcelable.Creator<NattKeepalivePacketData> CREATOR =
+            new Parcelable.Creator<NattKeepalivePacketData>() {
+                public NattKeepalivePacketData createFromParcel(Parcel in) {
+                    final InetAddress srcAddress =
+                            InetAddresses.parseNumericAddress(in.readString());
+                    final InetAddress dstAddress =
+                            InetAddresses.parseNumericAddress(in.readString());
+                    final int srcPort = in.readInt();
+                    final int dstPort = in.readInt();
+                    try {
+                        return NattKeepalivePacketData.nattKeepalivePacket(srcAddress, srcPort,
+                                    dstAddress, dstPort);
+                    } catch (InvalidPacketException e) {
+                        throw new IllegalArgumentException(
+                                "Invalid NAT-T keepalive data: " + e.error);
+                    }
+                }
+
+                public NattKeepalivePacketData[] newArray(int size) {
+                    return new NattKeepalivePacketData[size];
+                }
+            };
+}