Remove unused getTetherStats

Before Android R, getTetherStats were used to collect tethering
iface stats of all clients who extends ITetheringStatsProvider,
which typically contains NetdTetheringStatsProvider and
OffloadController.

However, this always returns 0 since Android R, because:
  1. OffloadController implemented NetworkStatsProvider and no
     longer reports stats through getTetherStats.
  2. NetdTetheringStatsProvider always return 0 by design since
     non-offloaded iface tethering stats are already included
     in native iface stats.

This change is a no-op refactoring to remove unused
getTetherStats and update test which is not pratical.
Fix for offloaded tethering stats will be in follow-up CLs.

Test: atest FrameworksNetTests TetheringTests
Bug: 162292214
Change-Id: Icd0717c5c2807ae3bd98626b897e4b148f142815
diff --git a/services/core/java/com/android/server/net/NetworkStatsService.java b/services/core/java/com/android/server/net/NetworkStatsService.java
index 12c24d4..96e3c51 100644
--- a/services/core/java/com/android/server/net/NetworkStatsService.java
+++ b/services/core/java/com/android/server/net/NetworkStatsService.java
@@ -1083,13 +1083,9 @@
         if (nativeIfaceStats == -1) {
             return nativeIfaceStats;
         } else {
-            // When tethering offload is in use, nativeIfaceStats does not contain usage from
-            // offload, add it back here.
-            // When tethering offload is not in use, nativeIfaceStats contains tethering usage.
-            // this does not cause double-counting of tethering traffic, because
-            // NetdTetheringStatsProvider returns zero NetworkStats
-            // when called with STATS_PER_IFACE.
-            return nativeIfaceStats + getTetherStats(iface, type);
+            // TODO: When tethering offload is in use, nativeIfaceStats does not contain usage from
+            //  offload, add it back here.
+            return nativeIfaceStats;
         }
     }
 
@@ -1100,42 +1096,7 @@
             return nativeTotalStats;
         } else {
             // Refer to comment in getIfaceStats
-            return nativeTotalStats + getTetherStats(IFACE_ALL, type);
-        }
-    }
-
-    private long getTetherStats(String iface, int type) {
-        final NetworkStats tetherSnapshot;
-        final long token = Binder.clearCallingIdentity();
-        try {
-            tetherSnapshot = getNetworkStatsTethering(STATS_PER_IFACE);
-        } catch (RemoteException e) {
-            Slog.w(TAG, "Error get TetherStats: " + e);
-            return 0;
-        } finally {
-            Binder.restoreCallingIdentity(token);
-        }
-        HashSet<String> limitIfaces;
-        if (iface == IFACE_ALL) {
-            limitIfaces = null;
-        } else {
-            limitIfaces = new HashSet<String>();
-            limitIfaces.add(iface);
-        }
-        NetworkStats.Entry entry = tetherSnapshot.getTotal(null, limitIfaces);
-        if (LOGD) Slog.d(TAG, "TetherStats: iface=" + iface + " type=" + type +
-                " entry=" + entry);
-        switch (type) {
-            case 0: // TYPE_RX_BYTES
-                return entry.rxBytes;
-            case 1: // TYPE_RX_PACKETS
-                return entry.rxPackets;
-            case 2: // TYPE_TX_BYTES
-                return entry.txBytes;
-            case 3: // TYPE_TX_PACKETS
-                return entry.txPackets;
-            default:
-                return 0;
+            return nativeTotalStats;
         }
     }
 
@@ -1429,14 +1390,6 @@
         final NetworkStats devSnapshot = readNetworkStatsSummaryDev();
         Trace.traceEnd(TRACE_TAG_NETWORK);
 
-        // Tethering snapshot for dev and xt stats. Counts per-interface data from tethering stats
-        // providers that isn't already counted by dev and XT stats.
-        Trace.traceBegin(TRACE_TAG_NETWORK, "snapshotTether");
-        final NetworkStats tetherSnapshot = getNetworkStatsTethering(STATS_PER_IFACE);
-        Trace.traceEnd(TRACE_TAG_NETWORK);
-        xtSnapshot.combineAllValues(tetherSnapshot);
-        devSnapshot.combineAllValues(tetherSnapshot);
-
         // Snapshot for dev/xt stats from all custom stats providers. Counts per-interface data
         // from stats providers that isn't already counted by dev and XT stats.
         Trace.traceBegin(TRACE_TAG_NETWORK, "snapshotStatsProvider");
@@ -1931,9 +1884,13 @@
     }
 
     /**
-     * Return snapshot of current tethering statistics. Will return empty
-     * {@link NetworkStats} if any problems are encountered.
+     * Return snapshot of current non-offloaded tethering statistics. Will return empty
+     * {@link NetworkStats} if any problems are encountered, or queried by {@code STATS_PER_IFACE}
+     * since it is already included by {@link #nativeGetIfaceStat}.
+     * See {@code OffloadTetheringStatsProvider} for offloaded tethering stats.
      */
+    // TODO: Remove this by implementing {@link NetworkStatsProvider} for non-offloaded
+    //  tethering stats.
     private NetworkStats getNetworkStatsTethering(int how) throws RemoteException {
         try {
             return mNetworkManager.getNetworkStatsTethering(how);