8212132: (dc) Remove DatagramChannelImpl finalize method

[Florian Weimer]

* Alan Bateman:

> Lots of good work in recent releases to replace the use of finalizers
> in the java.base module with the cleaner mechanism. The
> DatagramChannel implementation is still using a finalizer so it's time
> to replace that. While in the area I removed the wrapper around the
> cleaner used in the NIO SocketImpl as it is not needed.
>
> The proposed changes are here:
>   http://cr.openjdk.java.net/~alanb/8212132/webrev/index.html

What's the position on guarding against faillure in the cleaner
registration itself, sinde registerCleaner()?

Thanks,
Florian