i think the term pakki was, for a long time, when they first arrived here, largely prefixed with "fakkin pakki" or "pakkis go home" or some such, by white people, so it became an insult over time, even though it is just a shortened version.
n1gger is spelt and sort of pronounced n1ggA by black people so it's acceptable for them to use - it is their way of reclaiming the word for themselves and thereby demolishing its power as an offensive term.
i have heard "pakki's" call themselves that in bradford and think nothning of it - perhaps it is there way of reclaiming the word as their own again