Websockets: Scope ONE doesn't work correctly

Scope variable for data change listener is directly passed from notification subscription Rpc to data store listener. This causes unexpected behavior when registering notifications for scope 'ONE'.

For example if we listen on "nodes" container with scope 'ONE' expected behavior would be to get change events for individual nodes but we get nothing. This is because on yang data tree level, scope ONE would listen on "nodes" container and mixin MapNode "node" underneath it. Since this node is not representable in restconf we wont't get any notifications.