You don't need to install any drivers, i915 is already there.
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For the purposes of running a router, what you get without doing anything is almost certainly good enough, you won't see any difference in cli output anyways. If you still want to install the optional firmware requested by i915 for this chipset, the thread referenced by lleachii has all the (detailed) information about what to do, the file names might differ, but that you'll see in the logs - BUT AGAIN, you don't NEED to do anything, it will just workâ˘.