[syslinux] Using of pxelinux configfiles for both BIOS and UEFI boot

[Ady]

> Maybe the mentioned debate can be reopened since multi boot
> architecture are more common today? 
> 
 
Please, let's _not_ reopen this debate, yet again.

Every time someone tries network booting with mixed architectures / 
firmwares with Syslinux for the first time, we get to this discussion 
of using different filename extensions. Let's not waste time again.

There are at least 2 basic reasons to keep the same ".c32":

_ prior configuration files are re-usable, as-is, for whichever 
architecture supported by Syslinux;

_ in-common configuration files are used as-is.

To be clear, I am providing these 2 reasons for general information 
only, and this should not be interpreted as an open door for additional 
debate from my part. Of course, anyone is free to re-debate this until 
feeling nauseous, and my opinion is as valid as anyone's. I am just 
pointing out, as clear as I can, that this matter was discussed many 
times already, and the resolution has been implemented since version 
6.00(-pre).

FWIW, the ldlinux.{c32,e32,e64} modules _can_ be used in the same 
directory if so desired, together with {l,}pxelinux.0, bootx64.efi and 
bootia32.efi. So all this matter is only relevant when using additional 
modules.

Using dhcp options 209 and 210 should allow for 3 different initial 
configuration files, according to the architecture / firmware of the 
client.

Together with those 2 dhcp options, the (optional) usage of Syslinux 
directives such as:
PATH
INCLUDE
CONFIG

and the cmd.c32 module, there is enough flexibility for different types 
of users / cases.

If there is some case that is not covered, perhaps that's a matter of 
(lack of) documentation, and someone with experience might be able to 
provide / suggest / analyze specific alternatives. Let's focus on such 
particular case / situation.

Regards,
Ady.