crypto: testmgr - add guard to dst buffer for ahash_export

Add a guard to 'state' buffer and warn if its consistency after
call to crypto_ahash_export() changes, so that any write that
goes beyond advertised statesize (and thus causing potential
memory corruption [1]) is more visible.

[1] https://marc.info/?l=linux-crypto-vger&m=147467656516085



Signed-off-by: Jan Stancek <jstancek@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Marcelo Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>