[11u] RFR: 8250521 - Configure initial RTO to use minimal retry for loopback connections on Windows

[Mat Carter]

I'd like to propose the backport of JDK-8250521 and subsequent JDK-8255264 to 11u.

The patch applied cleanly but had no effect as 11u only used PlainSocketImpl whereas tip uses NIOSokectImpl, so I made comparable changes to PlainSocketImpl.

I kept the original changes to support NIOSocketImpl in case its ever backported.  However, I don't foresee pushing the changes to PlanSocketImpl to tip as its not used by default.

Passes all tier1 tests

JBS : https://bugs.openjdk.java.net/browse/JDK-8250521
Original fix: https://hg.openjdk.java.net/jdk/jdk/rev/035cdb28aa4c
Original webrev: https://cr.openjdk.java.net/~adityam/nikola/fast_connect_loopback_3/

JBS : https://bugs.openjdk.java.net/browse/JDK-8255264
Original fix: https://github.com/openjdk/jdk/commit/7e01bc96
Original PR: https://github.com/openjdk/jdk/pull/1523

webrev for 11u: http://cr.openjdk.java.net/~adityam/mat/8250521_jdk11/

Thanks in advance
Mat