[syslinux] PXELINUX: DHCP field giaddr (pxe_bootp_t.gip)

[Gene Cumm]

Right now, I almost have pxechn.c32 in a fully functional state by
adding a parameter to allow pure hex input of an option and its data.
It allows uppercase and lowercase entry with or without octet
delimiters (which must not match [0-9A-Fa-f]) and requires 2-digit
entry for the octet.  This is an extremely loose input format such
that users may utilize it in their preferred format.

After adding this, I believe I have about everything implemented
except I'm uncertain about the DHCP field giaddr (pxe_bootp_t.gip).
My current test environment doesn't utilize this (just 0).  I'm mostly
looking to see if it's something that it might be desirable to modify.
 DHCP fields sname and siaddr are already adjusted as needed.

-- 
-Gene