net/fd_windows.go:121: syscall.WSABuf composite literal uses unkeyed fields

Change-Id: I91cbe38199d5b6828379a854d08f6ceaf687dd82
Reviewed-on: https://go-review.googlesource.com/32760
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>