Save device secret

Device secret is needed for verification of auth tokens after device
restart.

BUG: 24110921
Change-Id: If956886fcd6325dd4b419b7ca39ccb6bc4708230
Reviewed-on: https://weave-review.googlesource.com/1180
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/libweave/src/privet/privet_manager.h b/libweave/src/privet/privet_manager.h
index 5e3df3f..a388967 100644
--- a/libweave/src/privet/privet_manager.h
+++ b/libweave/src/privet/privet_manager.h
@@ -83,6 +83,7 @@
   void OnConnectivityChanged();
 
   void OnHttpServerStatusChanged(const provider::HttpServer& server);
+  void SaveDeviceSecret(Config* config);
 
   bool disable_security_{false};
   std::unique_ptr<CloudDelegate> cloud_;