RFR 8200181 [11] Remove superflous non-IPv4 code from Java_java_net_TwoStacksPlainSocketImpl_socketListen

[Chris Hegarty]

Given that JDK-8058965 removed the IPv6 support from
TwoStacksPlainSocketImpl, the native socketListen method no longer
needs to deal with the non-IPv4 code path. This simplifies the code,
brings it in line with the unix variants, and removes a possible
problematic code path that could close the socket without notifying
the socket cleaner.

http://cr.openjdk.java.net/~chegar/8200181.00/
https://bugs.openjdk.java.net/browse/JDK-8200181

-Chris.

[1] https://bugs.openjdk.java.net/browse/JDK-8058965