Have f-test model

[amichuda]

     return np.nan

https://github.com/amichuda/statsmodels/blob/c74f4a6e3b593ad4c2ec4dc4adc1a36d8ab48cf4/statsmodels/regression/linear_model.py#L1853

Right now we don't fun a f-stat for the full model, but the statsmodels table has it. Setting it to np.nan for now.

[s3alfisc]

Yes, sounds good. We can have it once we have access to the full vcov matrix.

[s3alfisc]

Or, I actually implement a 'proper' bootstrapped Wald Tests, which is still on my to do list for fwildclusterboot 😄