iwn wlan connection losses after recent upgrade from 10-stable to head

Recently I upgraded my system to head from 10-stable:

11.0-CURRENT #0 r293760:
iwn0: <Intel Centrino Ultimate-N 6300> mem 0xe3c00000-0xe3c01fff irq 17 at
device 0.0 on pci2
net.wlan.debug: 1
net.wlan.0.debug: 1
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        ether 24:77:03:07:32:b8
        inet 192.168.254.21 netmask 0xffffff00 broadcast 192.168.254.255
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: IEEE 802.11 Wireless Ethernet MCS mode 11ng
        status: associated
        ssid SSID channel 1 (2412 MHz 11g ht/20) bssid 28:c6:8e:e6:04:7c
        country US authmode WPA2/802.11i privacy ON deftxkey UNDEF
        AES-CCM 2:128-bit AES-CCM 3:128-bit powersavemode CAM
        powersavesleep 100 txpower 13 bmiss 10 scanvalid 60 protmode CTS
        ampdulimit 64k ampdudensity 8 -amsdutx amsdurx shortgi wme
        roaming MANUAL
        groups: wlan


While the 10-STABLE setup was never a pillar of reliability, HEAD seems to
have made things worse for my wifi setup.  Now my connections drops out
several times a day at least resulting in logs such as this:

wpa_supplicant[81975]: wlan0: CTRL-EVENT-DISCONNECTED
bssid=28:c6:8e:e6:04:7c reason=0
kernel: wlan0: link state changed to DOWN
wpa_supplicant[81975]: wlan0: Trying to associate with 28:c6:8e:e6:04:7c
(SSID='SSID' freq=2412 MHz)
wpa_supplicant[81975]: wlan0: Authentication with 28:c6:8e:e6:04:7c timed
out.
wpa_supplicant[81975]: wlan0: CTRL-EVENT-DISCONNECTED
bssid=28:c6:8e:e6:04:7c reason=3 locally_generated=1
wpa_supplicant[81975]: wlan0: Trying to associate with 28:c6:8e:e6:04:7c
(SSID='SSID' freq=2412 MHz)
wpa_supplicant[81975]: wlan0: Authentication with 28:c6:8e:e6:04:7c timed
out.
wpa_supplicant[81975]: wlan0: CTRL-EVENT-DISCONNECTED
bssid=28:c6:8e:e6:04:7c reason=3 locally_generated=1
wpa_supplicant[81975]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=1
ssid="SSID" auth_failures=1 duration=10 reason=CONN_FAILED
wpa_supplicant[81975]: wlan0: CTRL-EVENT-SSID-REENABLED id=1 ssid="SSID"
wpa_supplicant[81975]: wlan0: Trying to associate with 28:c6:8e:e6:04:7c
(SSID='SSID' freq=2412 MHz)
wpa_supplicant[81975]: wlan0: Authentication with 28:c6:8e:e6:04:7c timed
out.
wpa_supplicant[81975]: wlan0: CTRL-EVENT-DISCONNECTED
bssid=28:c6:8e:e6:04:7c reason=3 locally_generated=1
wpa_supplicant[81975]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=1
ssid="SSID" auth_failures=2 duration=23 reason=CONN_FAILED
wpa_supplicant[81975]: wlan0: CTRL-EVENT-SSID-REENABLED id=1 ssid="SSID"
wpa_supplicant[81975]: wlan0: Trying to associate with 28:c6:8e:e6:04:7c
(SSID='SSID' freq=2412 MHz)
wpa_supplicant[81975]: wlan0: Authentication with 28:c6:8e:e6:04:7c timed
out.

Under 10-STABLE, such events were usually only a few times a week.

I've just disabled N to see if that helps, but is the decreased reliability
expected?  Is there anything I can do to improve stability and preserve N?

Thanks,

-- 
Adam