i decided not to waste any more time on this, i returned the dlink 865l and i got a tp-link wdr3600.
its has lower specs, only 300mbit on 2.4 and 5.0, but NAT work fine around 940 mb/sec and i can do
with wireless N for now, i have only one AC device, my phone.
i am really sorry for the d-link router, i had a 855 before 865L and it worked 5 years with no flows.
regarding the broadcom module that enables hardware nat its not open source, i couldn't find anything
helpful so i ended the search. one thing i can tell you, nobody that makes custom firmwares has this
feature running, so the only way to get support is from the manufacture.