telnet: allow programatic use on Windows

Summary of the issue can be found at:
http://curl.haxx.se/mail/lib-2010-04/0367.html

That patch only updated the unix sockets code - the winsock code was not
updated and no longer works the same was as the unix code. This change
updates the windows code accordingly.

Bug: http://curl.haxx.se/bug/view.cgi?id=3163118