Add network created callback support

Create a network callback to notify network agent after
netd has created the network, so that the NetworkAgent may
wait for this callback and ensure the pre-work to communicate
with netd completed.

Bug: 178725261
Test: make update-api
Change-Id: I8c2ff7bd6980ae838abc5669f9419d62741b8666
CTS-Coverage-Bug: 178725261

framework/api/system-current.txt

@@ -218,6 +218,7 @@ package android.net {
     method public void onAddKeepalivePacketFilter(int, @NonNull android.net.KeepalivePacketData);
     method public void onAutomaticReconnectDisabled();
     method public void onBandwidthUpdateRequested();
+    method public void onNetworkCreated();
     method public void onNetworkUnwanted();
     method public void onQosCallbackRegistered(int, @NonNull android.net.QosFilter);
     method public void onQosCallbackUnregistered(int);

framework/src/android/net/INetworkAgent.aidl

@@ -46,4 +46,5 @@ oneway interface INetworkAgent {
     void onRemoveKeepalivePacketFilter(int slot);
     void onQosFilterCallbackRegistered(int qosCallbackId, in QosFilterParcelable filterParcel);
     void onQosCallbackUnregistered(int qosCallbackId);
+    void onNetworkCreated();
 }

framework/src/android/net/NetworkAgent.java

@@ -361,6 +361,14 @@ public abstract class NetworkAgent {
      */
     public static final int CMD_UNREGISTER_QOS_CALLBACK = BASE + 21;
 
+    /**
+     * Sent by ConnectivityService to {@link NetworkAgent} to inform the agent that its native
+     * network was created and the Network object is now valid.
+     *
+     * @hide
+     */
+    public static final int CMD_NETWORK_CREATED = BASE + 22;
+
     private static NetworkInfo getLegacyNetworkInfo(final NetworkAgentConfig config) {
         final NetworkInfo ni = new NetworkInfo(config.legacyType, config.legacySubType,
                 config.legacyTypeName, config.legacySubTypeName);
@@ -560,6 +568,10 @@ public abstract class NetworkAgent {
                             msg.arg1 /* QoS callback id */);
                     break;
                 }
+                case CMD_NETWORK_CREATED: {
+                    onNetworkCreated();
+                    break;
+                }
             }
         }
     }
@@ -700,6 +712,11 @@ public abstract class NetworkAgent {
             mHandler.sendMessage(mHandler.obtainMessage(
                     CMD_UNREGISTER_QOS_CALLBACK, qosCallbackId, 0, null));
         }
+
+        @Override
+        public void onNetworkCreated() {
+            mHandler.sendMessage(mHandler.obtainMessage(CMD_NETWORK_CREATED));
+        }
     }
 
     /**
@@ -1009,6 +1026,11 @@ public abstract class NetworkAgent {
     protected void saveAcceptUnvalidated(boolean accept) {
     }
 
+    /**
+     * Called when ConnectivityService has successfully created this NetworkAgent's native network.
+     */
+    public void onNetworkCreated() {}
+
     /**
      * Requests that the network hardware send the specified packet at the specified interval.
      *