trivial patch to reduce allocations in nio open* methods

[Alan Bateman]

On 06/03/2018 18:34, Chris Hegarty wrote:
>
> It seems crummy, but using Set.of will require some care when
> handling duplicate options. The code currently silently ignores
> duplicates, if I'm not mistaken.
I just read Rémi's mail now. So yes, it could only use Set.of for 
options.length < 2.

-Alan