iPXE upstream (ipxe/ipxe@2161e976) now includes USB NIC drivers by
default in the all-drivers build. This disables BIOS SMM-based USB
legacy support which emulates a PS/2 keyboard, breaking USB keyboards
on some systems.
This adds support for building iPXE's `ipxe-legacy` driver set
variants which exclude USB NIC drivers, preserving USB keyboard
functionality for affected users.
New bootloader variants:
- Legacy BIOS: .lkrn, .dsk, .pdsk, .kpxe (with -legacy suffix)
- EFI: .efi (with -legacy suffix)
- Hybrid: .iso, .img (with -legacy suffix)
Controlled by the `generate_disks_legacy_usb` flag (default: true).
Agent-Logs-Url: https://github.com/netbootxyz/netboot.xyz/sessions/0337d14a-1d72-43d8-aa32-8a804eeac778
Co-authored-by: antonym <245007+antonym@users.noreply.github.com>