crypto: testmgr - expand serpent test vectors

AVX2 implementation of serpent cipher processes 16 blocks parallel, so
we need to make test vectors larger to check parallel code paths.
Signed-off-by: NJussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>