configure.in: include winsock2.h

* configure.in (NET_LUID): include winsock2.h instead of windows.h.
  patch by Jon Forums in [ruby-core:67125].  [Bug #10640]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48997 b2dd03c8-39d4-4d8f-98ff-823fe69b080e