The httptrace.ConnectStart and ConnectDone hooks are just about the
post-DNS connection to the host. We were accidentally also firing on
the UDP dials to DNS. Exclude those for now. We can add them back
later as separate hooks if desired. (but they'd only work for pure Go
DNS)

This wasn't noticed earlier because I was developing on a Mac at the
time, which always uses cgo for DNS. When running other tests on
Linux, I started seeing UDP dials.

Updates #12580

Change-Id: I2b2403f2483e227308fe008019f1100f6300250b
Reviewed-on: https://go-review.googlesource.com/23069Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>