noderes.netboot is parsed as grub2-<protocol> and validated with
/^http|tftp$/, which reads as (^http)|(tftp$) and so also accepts values
such as https, httpx and xtftp.
A value that passes but is not exactly "http" then falls through to
set root=$grub2protocol,$serverip, which drops site.httpport, so the mistake
surfaces as a confusing grub2 failure at boot instead of the "Invalid netboot
method" error this check exists to give. grub2-https cannot work in any case,
since only "insmod http" is emitted.
Supported values are unchanged: grub2, grub2-http and grub2-tftp.
Vinícius Ferrão