on amd64 r246552: iwn0: <Intel Wireless WiFi Link 4965>: fatal firmware error

This is a T61p 6459 laptop with (from pciconf -lv):

iwn0_at_pci0:3:0:0:        class=0x028000 card=0x11108086 chip=0x42308086 rev=0x61 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'PRO/Wireless 4965 AG or AGN [Kedron] Network Connection'
    class      = network

or (from dmesg):

iwn0: <Intel Wireless WiFi Link 4965> mem 0xdf2fe000-0xdf2fffff irq 17 at device 0.0 on pci3

I use it with

device          iwn             # Intel 4965/1000/5000/6000 wireless NICs.
device iwn4965fw

in the kernel.

>From time to time, and I think under some load, e.g. rsync a
partition in one windown and svn up /usr/ports in another,
I get this failure:

iwn0: iwn_intr: fatal firmware error
firmware error log:
  error type      = "NMI_INTERRUPT_WDG" (0x00000004)
  program counter = 0x0000046C
  source line     = 0x000000D0
  error data      = 0x0000000207030000
  branch link     = 0x00008370000004C2
  interrupt link  = 0x000006DA000018B8
  time            = 2858416859
driver status:
  tx ring  0: qid=0  cur=96  queued=0  
  tx ring  1: qid=1  cur=0   queued=0  
  tx ring  2: qid=2  cur=0   queued=0  
  tx ring  3: qid=3  cur=16  queued=0  
  tx ring  4: qid=4  cur=163 queued=0  
  tx ring  5: qid=5  cur=0   queued=0  
  tx ring  6: qid=6  cur=0   queued=0  
  tx ring  7: qid=7  cur=0   queued=0  
  tx ring  8: qid=8  cur=0   queued=0  
  tx ring  9: qid=9  cur=0   queued=0  
  tx ring 10: qid=10 cur=0   queued=0  
  tx ring 11: qid=11 cur=0   queued=0  
  tx ring 12: qid=12 cur=0   queued=0  
  tx ring 13: qid=13 cur=0   queued=0  
  tx ring 14: qid=14 cur=0   queued=0  
  tx ring 15: qid=15 cur=0   queued=0  
  rx ring: cur=14

I then have to restart the network via "/etc/rc.d/netif restart"
and it's back to normal.

>From ifconfig:

iwn0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 2290
        ether 00:21:5c:50:68:c3
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: IEEE 802.11 Wireless Ethernet autoselect mode 11g
        status: associated
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        ether 00:21:5c:50:68:c3
        inet 172.21.222.82 netmask 0xfffffc00 broadcast 255.255.255.255 
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: IEEE 802.11 Wireless Ethernet OFDM/48Mbps mode 11g
        status: associated
        ssid eduroam channel 1 (2412 MHz 11g) bssid 00:3a:98:62:cd:a0
        country US authmode WPA2/802.11i privacy ON deftxkey UNDEF
        AES-CCM 3:128-bit txpower 14 bmiss 10 scanvalid 450 bgscan
        bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
        wme roaming MANUAL

I use it with wpa_supplicant:

/usr/sbin/wpa_supplicant -s -B -i wlan0 -c /etc/wpa_supplicant.conf -D bsd -P /var/run/wpa_supplicant/wlan0.pid

Please advise

Thanks

Anton