ueagle-atm: fix PHY signal initialization race

ueagle-atm: fix PHY signal initialization race

A race exists when initializing ueagle-atm devices where the generic atm
device may not yet be created before the driver attempts to initialize
it's PHY signal state, which checks whether the atm device has been
created or not.  This often causes the sysfs 'carrier' attribute to be
'1' even though no signal has actually been found.

uea_probe
   usbatm_usb_probe
      driver->bind (uea_bind)
         uea_boot
            kthread_run(uea_kthread)     uea_kthread
      usbatm_atm_init                       uea_start_reset
         atm_dev_register                      UPDATE_ATM_SIGNAL

UPDATE_ATM_SIGNAL checks whether the ATM device has been created and if
not, will not update the PHY signal state.  Because of the race that
does not always happen in time, and the PHY signal state remains
ATM_PHY_SIG_FOUND even though no signal exists.

To fix the race, just create the kthread during initialization, and only
after initialization is complete, start the thread that reboots the
device and initializes PHY state.

[ 3030.490931] uea_probe: calling usbatm_usb_probe
[ 3030.490946] ueagle-atm 8-2:1.0: usbatm_usb_probe: trying driver ueagle-atm with vendor=1110, product=9031, ifnum  0
[ 3030.493691] uea_bind: setting usbatm
[ 3030.496932] usb 8-2: [ueagle-atm] using iso mode
[ 3030.497283] ueagle-atm 8-2:1.0: usbatm_usb_probe: using 3021 byte buffer for rx channel 0xffff880125953508
   <kthread already started before usbatm_usb_probe() has returned>
[ 3030.497292] usb 8-2: [ueagle-atm] (re)booting started
   <UPDATE_ATM_SIGNAL checks whether ATM device has been created yet before setting PHY state>
[ 3030.497298] uea_start_reset: atm dev (null)
   <and since it hasn't been created yet PHY state is not set>
[ 3030.497306] ueagle-atm 8-2:1.0: usbatm_usb_probe: using 3392 byte buffer for tx channel 0xffff8801259535b8
[ 3030.497374] usbatm_usb_probe: about to init
[ 3030.497379] usbatm_usb_probe: calling usbatm_atm_init
   <atm device finally gets created>
[ 3030.497384] usbatm_atm_init: creating atm device!

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>