During port updates, if the user does not pass address bindings,
nsxlib should perform a LP GET on the backend and use the
existing address bindings.
The response body returns address bindings in a dict format
which breaks the update in _build_attrs method. This patch
adds a new method which will convert the address bindings
dict into PacketAddressClassifier namedtuple.
Change-Id: I660cc63264d1458d17d587555889974571960bd5