Define TAG_SYSTEM_DNS

Define a traffic tag for dns so that apps know that the traffic
is not sent by them but is sent by the system on their behalf.

Test: Build
Bug: 132125333
Change-Id: I273112c5384999f3155a47f9e7e7cecdd33baa1a
diff --git a/core/java/com/android/internal/util/TrafficStatsConstants.java b/core/java/com/android/internal/util/TrafficStatsConstants.java
index 2806ae2..413be48 100644
--- a/core/java/com/android/internal/util/TrafficStatsConstants.java
+++ b/core/java/com/android/internal/util/TrafficStatsConstants.java
@@ -40,4 +40,5 @@
     // {@link android.net.TrafficStats#TAG_NETWORK_STACK_IMPERSONATION_RANGE_START} and
     // {@link android.net.TrafficStats#TAG_NETWORK_STACK_IMPERSONATION_RANGE_END}.
     public static final int TAG_SYSTEM_PROBE = 0xFFFFFF81;
+    public static final int TAG_SYSTEM_DNS = 0xFFFFFF82;
 }