Add ConnectivityManager.getActiveNetwork().
Rework NetID allocation in ConnectivityService so registerNetworkAgent() can
return the allocated NetID.

Bug: 19416463
Change-Id: I68e395552cf27422c80b4dfae5db5d56a0d68f5d
diff --git a/services/core/java/com/android/server/connectivity/Vpn.java b/services/core/java/com/android/server/connectivity/Vpn.java
index 0896955..d9c96f2 100644
--- a/services/core/java/com/android/server/connectivity/Vpn.java
+++ b/services/core/java/com/android/server/connectivity/Vpn.java
@@ -17,9 +17,10 @@
 package com.android.server.connectivity;
 
 import static android.Manifest.permission.BIND_VPN_SERVICE;
-import static android.os.UserHandle.PER_USER_RANGE;
+import static android.net.ConnectivityManager.NETID_UNSET;
 import static android.net.RouteInfo.RTN_THROW;
 import static android.net.RouteInfo.RTN_UNREACHABLE;
+import static android.os.UserHandle.PER_USER_RANGE;
 import static android.system.OsConstants.AF_INET;
 import static android.system.OsConstants.AF_INET6;
 
@@ -339,6 +340,10 @@
         return mNetworkInfo;
     }
 
+    public int getNetId() {
+        return mNetworkAgent != null ? mNetworkAgent.netId : NETID_UNSET;
+    }
+
     private LinkProperties makeLinkProperties() {
         boolean allowIPv4 = mConfig.allowIPv4;
         boolean allowIPv6 = mConfig.allowIPv6;