[NS05] Feed network offer callbacks

The design is very simply expressed :
An offer is needed for a request if and only if that offer
might beat the satisfier for that request.

The implementation of "might beat" is NetworkRanker#mightBeat.

Test: FrameworksNetTests FrameworksWifiTests NetworkStackTests
Bug: 167544279
Merged-In: I3c2563d4ae4e3715d0c6270344ba8f7ef067872f
Merged-In: I0fe911eef2483ecbac48c733d56283b81538690a
Change-Id: I0fe911eef2483ecbac48c733d56283b81538690a
  (cherry-picked from 7b6a33bd504e88ac051db9511eafe915d80e7539)
diff --git a/framework/api/system-current.txt b/framework/api/system-current.txt
index 27bf114..f8ffb58 100644
--- a/framework/api/system-current.txt
+++ b/framework/api/system-current.txt
@@ -316,9 +316,16 @@
     method public int getProviderId();
     method public void onNetworkRequestWithdrawn(@NonNull android.net.NetworkRequest);
     method public void onNetworkRequested(@NonNull android.net.NetworkRequest, @IntRange(from=0, to=99) int, int);
+    method @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY) public void registerNetworkOffer(@NonNull android.net.NetworkScore, @NonNull android.net.NetworkCapabilities, @NonNull java.util.concurrent.Executor, @NonNull android.net.NetworkProvider.NetworkOfferCallback);
+    method @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY) public void unregisterNetworkOffer(@NonNull android.net.NetworkProvider.NetworkOfferCallback);
     field public static final int ID_NONE = -1; // 0xffffffff
   }
 
+  public static interface NetworkProvider.NetworkOfferCallback {
+    method public void onNetworkNeeded(@NonNull android.net.NetworkRequest);
+    method public void onNetworkUnneeded(@NonNull android.net.NetworkRequest);
+  }
+
   public class NetworkReleasedException extends java.lang.Exception {
   }