Only connect to one address per address family.

This ensures probes don't take too long when a host has
multiple addresses. So for example:

$ adb shell settings put global captive_portal_http_url http://play.googleapis.com/generate_204
$ host play.googleapis.com
play.googleapis.com is an alias for googleapis.l.google.com.
googleapis.l.google.com has address 216.58.196.234
googleapis.l.google.com has address 216.58.197.10
googleapis.l.google.com has address 172.217.26.106
googleapis.l.google.com has address 172.217.27.170
googleapis.l.google.com has address 216.58.199.234
googleapis.l.google.com has address 216.58.221.170
googleapis.l.google.com has IPv6 address 2404:6800:400a:807::200a

results in:

06-29 21:38:09.695 - PROBE_DNS play.googleapis.com 270ms OK 2404:6800:400a:806::200a,172.217.26.106

Bug: 36532213
Test: as described in commit description
Change-Id: I6779a8356bac8d4a3912b0822379d45dfc662541