Do not register callback for < MIN_THRESHOLD_BYTES

This also avoids returning a nonzero multipath preference
if remaining data is low but nonzero.

Bug: b/72877610
Change-Id: I2459ded06de77d284ae1fe81a60d9e1df56b0c26
Fixes: b/72877610
Test: Tests in go/ag/3842960 pass

core/java/android/app/usage/NetworkStatsManager.java

@@ -35,6 +35,7 @@ import android.os.Messenger;
 import android.os.RemoteException;
 import android.os.ServiceManager;
 import android.os.ServiceManager.ServiceNotFoundException;
+import android.util.DataUnit;
 import android.util.Log;
 
 import com.android.internal.annotations.VisibleForTesting;
@@ -95,6 +96,15 @@ public class NetworkStatsManager {
     /** @hide */
     public static final int CALLBACK_RELEASED = 1;
 
+    /**
+     * Minimum data usage threshold for registering usage callbacks.
+     *
+     * Requests registered with a threshold lower than this will only be triggered once this minimum
+     * is reached.
+     * @hide
+     */
+    public static final long MIN_THRESHOLD_BYTES = DataUnit.MEBIBYTES.toBytes(2);
+
     private final Context mContext;
     private final INetworkStatsService mService;