Tweak bench-slope parameters
* tests/bench-slope.c (BUF_STEP_SIZE): Half step size to 64. (NUM_MEASUREMENT_REPETITIONS): Double repetitions to 64.
Tweak parameters for better repeatability of results with fast ciphers
(AES-NI).
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>