MLX5E_MAX_RQ_NUM_MTTS should be the maximum value, so that
MLX5_MTT_OCTW(MLX5E_MAX_RQ_NUM_MTTS) fits into u16. The current value of
1 << 17 results in MLX5_MTT_OCTW(1 << 17) = 1 << 16, which doesn't fit
into u16. This commit replaces it with the maximum value that still
fits u16.