RFR : 8024952 : ClassCastException in PlainSocketImpl.accept() when using custom socketImpl

[Seán Coffey]

Looking for review on recently reported issue. Issue seen on windows 
when a custom socketImpl is in use.

bug report : https://bugs.openjdk.java.net/browse/JDK-8024952
webrev : http://cr.openjdk.java.net/~coffeys/webrev.8024952/webrev/
Regards,
Sean.