8220738: (sc) Move ServerSocketChannelImpl remaining native method to Net

[Alan Bateman]

ServerSocketChannelImpl has one remaining native method, accept0, to 
accept connections. I'd like to move this to sun.nio.ch.Net so that 
ServerSocketChannelImpl.c to be removed, along with native methods in 
SctpServerChannelImpl and UnixAsynchronousServerSocketChannelImpl that 
wrap it. This is the last of the "move native method" changes that are 
needed for NIO based SocketImpl that I mentioned in other mails.

At one point, someone added a wrapper in ServerSocketChannelImpl to 
facilitate instrumentation, I can't quite tell what this was for but the 
instrumentation in JFR does not use it so I think it is safe to remove.

One of the SCTP tests doesn't compile since it was changed to use 
InetAddress.getLoopbackAddress so that is fixed too.

The webrev with the changes is here:
    http://cr.openjdk.java.net/~alanb/8220738/webrev/index.html

-Alan