Add a binder RPC to enable/disable data saver.

Bug: 26685616
Bug: 27506285
Change-Id: Id11ee717cfc1c79070b6bbec397986c25947646c
diff --git a/server/NetdNativeService.h b/server/NetdNativeService.h
index b24e96e..f7409d8 100644
--- a/server/NetdNativeService.h
+++ b/server/NetdNativeService.h
@@ -36,6 +36,7 @@
     binder::Status firewallReplaceUidChain(
             const String16& chainName, bool isWhitelist,
             const std::vector<int32_t>& uids, bool *ret) override;
+    binder::Status bandwidthEnableDataSaver(bool enable, bool *ret) override;
 
 };