iwn(4) crashing when wlan device is brought up, CA-N-6200

Hi all,

I just bought a Centrino Advanced N-6200 mini-pcie card because it should be 
supported by iwn(4) -- unfortunately it leads to a kernel panic the instant I 
try to do

# ifconfig wlan0 up

The creation of wlan0 on top of iwn0 works. Here are the (I hope) most 
relevant exerpts from core.txt:

FreeBSD photon.home.palmen-it.de 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r275075: 
Wed Nov 26 11:06:23 CET 2014     root_at_photon.home.palmen-
it.de:/usr/obj/usr/src/sys/NODEBUG  amd64

dmesg:
[...]
iwn0: <Intel Centrino Advanced-N 6200> mem 0xf0200000-0xf0201fff at device 0.0 
on pci1
wlan0: Ethernet address: 00:27:c1:03:a0:89
iwn0: iwn_read_firmware: ucode rev=0x09dd0401
iwn0: iwn_intr: fatal firmware error
iwn_fatal_intr: bad firmware error log address 0x00000000
iwn0: iwn_panicked: controller panicked, iv_state = 0; resetting...
iwn0: iwn_read_firmware: ucode rev=0x09dd0401
iwn0: iwn_hw_init: timeout waiting for adapter to initialize, error 35
iwn0: iwn_init_locked: could not initialize hardware, error 35
iwn0: iwn5000_post_alive: could not configure WiMAX coexistence, error 35

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address	= 0xffffffffffffffe0
fault code		= supervisor write data, page not present
instruction pointer	= 0x20:0xffffffff809a300a
stack pointer	        = 0x28:0xfffffe0107cdda70
frame pointer	        = 0x28:0xfffffe0107cddaa0
code segment		= base 0x0, limit 0xfffff, type 0x1b
			= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags	= interrupt enabled, resume, IOPL = 0
current process		= 0 (iwn0 net80211 taskq)
trap number		= 12

stacktrace:
(kgdb) #0  doadump (textdump=<value optimized out>) at pcpu.h:219
#1  0xffffffff80962918 in kern_reboot (howto=260)
    at /usr/src/sys/kern/kern_shutdown.c:447
#2  0xffffffff80962e40 in panic (fmt=<value optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:746
#3  0xffffffff80dae65f in trap_fatal (frame=<value optimized out>, 
    eva=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:866
#4  0xffffffff80dae9ac in trap_pfault (frame=0xfffffe0107cdd9c0, 
    usermode=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:677
#5  0xffffffff80dadfce in trap (frame=0xfffffe0107cdd9c0)
    at /usr/src/sys/amd64/amd64/trap.c:426
#6  0xffffffff80d90342 in calltrap ()
    at /usr/src/sys/amd64/amd64/exception.S:231
#7  0xffffffff809a300a in firmware_put (p=0x0, flags=1)
    at /usr/src/sys/kern/subr_firmware.c:367
#8  0xffffffff82638c58 in iwn_init_locked (sc=0xfffffe0002599000)
    at /usr/src/sys/modules/iwn/../../dev/iwn/if_iwn.c:8646
#9  0xffffffff82633e3c in iwn_ioctl (ifp=<value optimized out>, 
    cmd=<value optimized out>, data=<value optimized out>)
    at /usr/src/sys/modules/iwn/../../dev/iwn/if_iwn.c:4924
#10 0xffffffff809b4975 in taskqueue_run_locked (queue=0xfffff80005efe900)
    at /usr/src/sys/kern/subr_taskqueue.c:356
#11 0xffffffff809b5788 in taskqueue_thread_loop (arg=<value optimized out>)
    at /usr/src/sys/kern/subr_taskqueue.c:623
#12 0xffffffff8092aa8a in fork_exit (
    callout=0xffffffff809b56c0 <taskqueue_thread_loop>, 
    arg=0xfffffe0001de70f0, frame=0xfffffe0107cddc00)
    at /usr/src/sys/kern/kern_fork.c:977
#13 0xffffffff80d9087e in fork_trampoline ()
    at /usr/src/sys/amd64/amd64/exception.S:605
#14 0x0000000000000000 in ?? ()

I pasted the complete core.txt here: http://pastebin.com/KipkYx1y

Best regards,
Felix