8198372: API to create a SelectableChannel to a FileDescriptor

[Chris Hegarty]

What I meant to say:

I don't think that a default implementation is needed here,
or even how one could be written without making a number of
assumptions. Close, just like read and write, needs to be
handled by whatever external entity is interested in the
readiness information. The callback to coordinate closure
with the Selector is required to safely de-register
registered channels. I think this is fine as is.

-Chris.