Correct e1000 interrupt routine to enable on 1 disable on 0. duh.
The e1000_irq() routine should (per mcb30) do enable on non-zero,
disable on zero. This is not consistent in all drivers, so I'll
wait to update it when doing a global sweep.
There may still be an issue with memory handling, since it seems to
die ungracefully when ARP packets come in after loading a kernel.
Something to debug.