[Django] nplusone complains both with and without prefetch_related

Hi!

I have a case where nplusone first complains that a `prefetch_related` is missing and once I add that it complains that the new `prefetch_related` is over-eager.

In more detail:
- The related part of the model is:
- Three Models: P, N and U
- Query starts at P, i.e. `P.objects.[..]`
- P has an m2m relation to N
- N has a foreign key towards U
- Initial error is:
`Potential n+1 query detected on "N.u"`
- Once I add `.prefetch_related('n__u')` it changes to:
`Potential unnecessary eager load detected on "P.n"`

Any thoughts other than whitelisting for a workaround?

Thanks in advance!