grml2usb result in the ssh boot option buried right in the middle

[suntong]

Migrated from https://github.com/grml/grml/, please see the details at grml/grml#169

Basically,

better move the ssh to the end of the boot option for grml2usb

• Originally reported based on grml64-full release 2020.06
• Verified with grml2usb from grml64-full release 2021.07 and the problem persists.