NetworkStatsService to adjust VPN stats before recording.

* Creates a new Parcelable class VpnInfo to hold required
  parameters for VPN stats adjustments.
* ConnectivityService to collect infomation and provide
  a list of VpnInfo, one for each user.
* NetworkStatsService passes the VpnInfo array to
  NetworkStatsRecorder.
* NetworkStatsRecorder calls NetworkStats.migrateTun()
  to do the math.
* Poll NetworkStats when the vpn application calls
  setUnderlyingNetworks().

Bug: 19536273
Change-Id: I7a4c7726b8243fead10416f7ec6eb5cf95f20183

core/java/android/net/IConnectivityManager.aidl

@@ -33,6 +33,7 @@ import android.os.ResultReceiver;
 
 import com.android.internal.net.LegacyVpnInfo;
 import com.android.internal.net.VpnConfig;
+import com.android.internal.net.VpnInfo;
 import com.android.internal.net.VpnProfile;
 
 /**
@@ -116,6 +117,8 @@ interface IConnectivityManager
 
     LegacyVpnInfo getLegacyVpnInfo();
 
+    VpnInfo[] getAllVpnInfo();
+
     boolean updateLockdownVpn();
 
     void captivePortalCheckCompleted(in NetworkInfo info, boolean isCaptivePortal);