MFC 196745:

MFC 196745:
Don't attempt to bind the current thread to the CPU an IRQ is bound to
when removing an interrupt handler from an IRQ during shutdown.  During
shutdown we are already bound to CPU 0 and this was triggering a panic.

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@196996 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f