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: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>