Fix 5 bugs:

Fix 5 bugs:
	1) always call fxp_stop in fxp_detach.  Since we don't read from
	   the card, there's no need to carefully look at things with
	   bus_child_present.
	2) Call FXP_UNLOCK() before calling bus_teardown_intr to avoid
	   a possible deadlock reported by jhb.
	3) add gone to the softc.  Set it to true in detach.
	4) Return immediately if gone is true in fxp_ioctl
	5) Return immediately if gone is true in fxp_intr