- Call ether_ifdetach() before shutting down the hardware. - Remove a useless device_is_alive() check. - Disable interrupts if bus_child_present() so that this   check is more useful.
- Call ether_ifdetach() before shutting down the hardware.
- Remove a useless device_is_alive() check.
- Disable interrupts if bus_child_present() so that this
  check is more useful.

This fixes the hangs I was seeing when unloading the fxp driver.

Suggestions from:	hsu, njl

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