Increase ndarray fast path dispatch ndim limit to 5D.

A user noticed that array >=4D is significantly slower in a low work intensity function.  This is due to the cutoff limit in the dispatching code at 4D.  This patch increases the fast path to include up to 5D.  In the future, we can set the "N_NDIM" macro to a higher number to allow high dimension array for the fast path.