- Fix locking problem with optics module interrupts: ifmedia_add()
  may block on memory allocation, and so it cannot be safely done from
  a softint nor can it be done while holding a spin lock.  Fix this by
  using a workqueue rather than a softint, and hold the IFNET_LOCK
  across the entire handler, and the CORE_LOCK only across the code that
  needs to serialize access to the hardware state.
- Use ifmedia_fini().

Tested in a variety of devices by msaitoh@.  (Thanks!)

(thorpej)