Use unzip -o rather than unzip -u when extracting the kernel to use
with stboot; -u (update) leaves any existing and stale file unchanged,
and we probably have no reliable timestamps needed for a working
update operation.

Add the igb.ko driver and its dependencies to the initramfs
qemu-iso-boot-from-net.sh script. That makes the resulting image boot
on our supermicro test machine.