In general the package net deals IPv4 addresses as IPv6 IPv4-mapped
addresses internally for the dual stack era, when we need to support
various techniques on IPv4/IPv6 translation.

This change makes windows implementation follow the same pattern which
BSD variants and Linux do.

Updates #13544.

Also fixes an unintentionally formatted line by accident by gofmt.

Change-Id: I4953796e751fd8050c73094468a0d7b0d33f5516
Reviewed-on: https://go-review.googlesource.com/17992Reviewed-by: Alex Brainman <alex.brainman@gmail.com>