The file you need to edit is: /etc/default/grub (NOT /boot/grub/grub.cfg, sorry)
Mine has: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash irqpoll"
Run 'update-grub' afterwards to update /boot/grub/grub.cfg. And then reboot the PC and re-run the EDMA interrupt test.
Regards, Eric