Accumulate network statistics based on deltas.

Network stats are now read out of the kernel in one sweep, instead of
reading per-UID.  We now accumulate the delta traffic between each
stats snapshot using the well-tested SamplingCounter pattern.

Since Wi-Fi and mobile traffic have different costs, track each
separately.  Avoids counting misc interfaces like loopback and
ethernet under total.

Bug: 5543387
Change-Id: I642004dc530113c27ef79f2abbae51d8af30117f

core/java/android/net/ConnectivityManager.java

@@ -463,6 +463,21 @@ public class ConnectivityManager {
         }
     }
 
+    /**
+     * Checks if the given network type is backed by a Wi-Fi radio.
+     *
+     * @hide
+     */
+    public static boolean isNetworkTypeWifi(int networkType) {
+        switch (networkType) {
+            case TYPE_WIFI:
+            case TYPE_WIFI_P2P:
+                return true;
+            default:
+                return false;
+        }
+    }
+
     /**
      * Specifies the preferred network type.  When the device has more
      * than one type available the preferred network type will be used.