dhclient fails for iwn0 when no security

[Andrew Cagney <andrew.cagney%gmail.com@localhost>]

NetBSD 7.0.1 fresh install and the iwn0 device (forgive typos):

iwn0 at pci1 dev 0 function 0: vendor 0x8086 product 0x0091 (rev. 0x34)
iwn0: interrupting at ioapic0 pin 16
iwn0: MIMO 2T2R, MoW, address ...
iwn0: 11a rates: ....

I'm finding that when I'm connecting to a public network (such as the
one at a recent BSD conference), my DHCP requests seemingly fall on
deaf ears.  Using TCPDUMP I could see:

- the requests supposedly going out
- no replies
- lots of other traffic on that network (which suggests to me that
I've associated)

Getting another machine to sniff for packets from this machine didn't
show up anything (but that isn't really a good indicator).

The strange thing is that when pointed at a network with
key_mgmt=WPA-PSK then things do work.

Any hints?  Try again next year :-)

Andrew