In a former version of ng_bridge(4) the exernal visible host entry
structure was a strict subset of the internal one. So internal view
was direct annotation of the external structure. This strict
inheritance was gone many versions ago. There is no need to
encapsulate a part of the internal represntation as a separate
This patch is a preparation to make the internal structure read only
in the data path in order to make ng_bridge(4) multithreaded.