pdh.dll is not available on Windows IoT core. Use netevent.dll instead.

Update golang/go#26148

Change-Id: I80c299ad030944954d5d7d182d91dc15e71341f9
Reviewed-on: https://go-review.googlesource.com/c/154560Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>