network-address test: add ipv6-fail ipv4-slow case

Add a case for when the IPv6 result comes back negative and the IPv4
result is significantly delayed.  This is exactly the case that causes
the bug addressed by !865
10 jobs for wip/desrt/happier-eyeballs in 22 minutes (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #318038
cross-android_api21_arm64

00:02:21

passed #318039
cross-android_api28_arm64

00:02:21

passed #318040
cross-mingw64

00:03:31

passed #318036
debian-stable-x86_64

00:03:02

passed #318035
fedora-x86_64

00:06:56

passed #318043
freebsd-11
freebsd-11-x86_64

00:03:50

passed #318037
G_DISABLE_ASSERT

00:03:29

passed #318041
win32
msys2-mingw32

00:09:47

passed #318042
win32
vs2017-x64

00:09:23

 
  Coverage
passed #318044
coverage

00:01:25

78.1%