tcp: avoid sending dup ack if FIN already been acked by user event
tcp: avoid sending dup ack if FIN already been acked by user event

ingve/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,mnordsletten/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,AnnikaH/IncludeOS,mnordsletten/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,alfred-bratterud/IncludeOS,hioa-cs/IncludeOS,AnnikaH/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,ingve/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,alfred-bratterud/IncludeOS,hioa-cs/IncludeOS,ingve/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,AnnikaH/IncludeOS