bin/51379: dhcpcd connects to open wifi networks

[coypu%sdf.org@localhost]

>Number:         51379
>Category:       bin
>Synopsis:       dhcpcd connects to open wifi networks
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jul 30 09:00:00 +0000 2016
>Originator:     coypu
>Release:        NetBSD  7.99.34
>Organization:
>Environment:
NetBSD  7.99.34 NetBSD 7.99.34 (GENERIC.201607261420Z) amd64
dhcpcd 6.11.1
>Description:
I don't think it's desirable to connect to an open wifi network
just because one exists, but it seems to happen:

detach USB wifi, attach again, call dhcpcd.
notice USB wifi light go on after dhcpcd called, because:

# rm /var/db/dhcpcd-*
# dhcpcd -B
DUID 00:01:00:01:1e:d9:fe:15:fc:aa:14:71:53:60
alc0: IAID a2:96:50:45
urtwn0: waiting for carrier
alc0: soliciting a DHCP lease
alc0: soliciting an IPv6 router
alc0: offered 10.0.0.2 from 10.0.0.138
alc0: leased 10.0.0.2 for 3600 seconds
alc0: adding route to 10.0.0.0/24
alc0: adding default route via 10.0.0.138
urtwn0: carrier acquired
urtwn0: adding address fe80::c3ec:5ed3:50e1:3831
urtwn0: IAID 38:5b:6c:6c
urtwn0: soliciting an IPv6 router
urtwn0: soliciting a DHCP lease
alc0: no IPv6 Routers available
urtwn0: offered 192.168.168.5 from 192.168.168.254
urtwn0: leased 192.168.168.5 for 1800 seconds
urtwn0: adding route to 192.168.168.0/24
urtwn0: no IPv6 Routers available

It connected to an open wifi network (which is not mine, either).
>How-To-Repeat:

>Fix: