DHCP to support both legacy and UEFI mode

Example dhcpd.conf

 next-server 192.168.0.53;
 if option arch = 00:06 {
 filename "uefi32.efi";
 } else if option arch = 00:07 {
 filename "uefi64.efi";
 } else if option arch = 00:09 {
 filename "uefi64.efi";
 } else {
 filename "default.pxe";
 }