Michael Brown
efd322091d
Set up %ds *before* testing a value in our data segment (d'oh!).
Always send EOI; do not chain to BIOS's default interrupt handler.
They are just too unpredictable; at least VMware's seems to kill the
machine if you go anywhere near it.
Disable interrupts after return from PXENV_UNDI_ISR, just in case some
dumb PXE stack enables them.