Wrong handling of leaf-ref leaves that are pointing to an identity-ref

If there is a leaf of type leafref and is pointing to a leaf with identity-ref type. It is not parsed correctly in restconf, since the prefix is ignored.

This prevents the reconfiguration and spawning of config modules via Restconf according to e.g. https://wiki.opendaylight.org/view/OpenDaylight_Controller:Config:Examples:Netconf#Spawning_Additional_Netconf_Connectors_While_the_Controller_is_Running