Comment 18 for bug 1811496

Another issue was that 20_ipxe didn't call save_default_entry, to save the selected grub entry for subsequent reboots.

Since it was only a 2-line diff in the same spot, I added it as a second commit.

I also built the package in https://code.launchpad.net/~ts.sch.gr/+recipe/ipxe in case anyone needs it for previous Ubuntu versions.