pxe, e1000 and qemu-kvm 1.6 workaround

With the last update in Debian of qemu-kvm to version 1.6, booting vms via pxe with the e1000 (and ne2k_pci) network cards is no working anymore. I didn't take a deep look of the issue yet, but there is an easy solution (actually 2) for that.

Easiest one:
    wget https://github.com/qemu/qemu/raw/master/pc-bios/pxe-e1000.rom -O /usr/lib/ipxe/e1000_82540.rom 

Another one:
    git clone http://git.ipxe.org/ipxe.git 
    cd ipxe/src 
    make bin/8086100e.rom 
    cp bin/8086100e.rom /usr/lib/ipxe/e1000_82540.rom