Update netboot.xyz.lkrn to v2.0.72, supporting Grml 2022.11 release

Update netboot.xyz.lkrn to v2.0.72, supporting Grml 2022.11 release

See https://github.com/netbootxyz/netboot.xyz/commit/a4836eaba203a4b45ccf16a65d1b75fb57cd1d4a

Retrieved via:

| % wget -q https://github.com/netbootxyz/netboot.xyz/releases/download/2.0.72/netboot.xyz.efi
| % wget -q https://github.com/netbootxyz/netboot.xyz/releases/download/2.0.72/netboot.xyz.lkrn
| % wget -q https://github.com/netbootxyz/netboot.xyz/releases/download/2.0.72/netboot.xyz-sha256-checksums.txt
| % sha256sum -c netboot.xyz-sha256-checksums.txt 2>/dev/null | grep -e 'netboot.xyz.efi:' -e 'netboot.xyz.lkrn:'
| netboot.xyz.efi: OK
| netboot.xyz.lkrn: OK

Currently fails to boot Grml though, see
https://github.com/netbootxyz/netboot.xyz/issues/1310