[netdrvr skfddi] use PCI hotplug API; other cleanups

Third revision of the cleanup of skfddi driver.
  * use new pci device bus initialization
  * allocate network device with alloc_fddidev and use dev->priv
   * get rid of special module/non module distinctions.
   * fix error unwinds and return values on initialization
   * call driver_init directly not via register_netdev
   * reset internal queue count after purge
   * get rid of h[iy]sterical comment that is no longer true
     about warnings