Refactor tetherGetStats by using stable aidl structure

Use stable aidl structure instead of persistbundle

Test: built, flashed, booted
      system/netd/tests/runtests.sh passes

Change-Id: Id48cea4da4f9f4406ceb3d2281a5cfaaea8ce24f
diff --git a/server/NetdNativeService.h b/server/NetdNativeService.h
index 89c04f7..4da1335 100644
--- a/server/NetdNativeService.h
+++ b/server/NetdNativeService.h
@@ -94,7 +94,8 @@
 
     // Tethering-related commands.
     binder::Status tetherApplyDnsInterfaces(bool *ret) override;
-    binder::Status tetherGetStats(android::os::PersistableBundle *ret) override;
+    binder::Status tetherGetStats(
+            std::vector<android::net::TetherStatsParcel>* tetherStatsVec) override;
     binder::Status tetherStart(const std::vector<std::string>& dhcpRanges) override;
     binder::Status tetherStop() override;
     binder::Status tetherIsEnabled(bool* enabled) override;