libweave: Extract weave::Settings struct

This will help to avoid a log of getters in BuffetConfig interface.

BUG=brillo:1242
TEST='FEATURES=test emerge-gizmo buffet'

Change-Id: I76399760d77df950c6471d113f8cc0671faaa040
Reviewed-on: https://chromium-review.googlesource.com/286591
Trybot-Ready: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/manager.h b/buffet/manager.h
index feb6b9d..6db50fe 100644
--- a/buffet/manager.h
+++ b/buffet/manager.h
@@ -102,7 +102,7 @@
 
   void OnStateChanged();
   void OnRegistrationChanged(weave::RegistrationStatus status);
-  void OnConfigChanged(const weave::BuffetConfig& config);
+  void OnConfigChanged(const weave::Settings& settings);
   void UpdateWiFiBootstrapState(weave::WifiSetupState state);
   void OnPairingStart(const std::string& session_id,
                       weave::PairingType pairing_type,