drbd: debug: limit nelink-broadcast of request on digest mismatch to 32k

We used to be limited to 32k requests,
but have increased that limit to 128k now.

This part of the code can only deal with 32k,
it would scramble arbitrary pages for larger requests.

As it is used for debugging only anyways,
it is ok to simply truncate the dumped data here.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>