vendor: re-vendor golang.org/x/net to fix Dragonfly build

vendor: re-vendor golang.org/x/net to fix Dragonfly build

This picks up CL 202317 which fixes golang.org/x/net for Dragonfly
master (upcoming 5.8 release). Also re-enable the interface tests
disabled in CL 201482.

Vendored using:

    $ go get golang.org/x/net@24d2ffbea1e8
    $ go mod tidy
    $ go mod vendor

Fixes #34368

Change-Id: Iac152b7ffaa607bfedbb4024b4e1ffc9b649d689
Reviewed-on: https://go-review.googlesource.com/c/go/+/202438
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>