crypto: testmgr - check for skcipher_request corruption

Check that algorithms do not change the skcipher_request structure, as
users may rely on submitting the request again (e.g. after copying new
data into the same source buffer) without reinitializing everything.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>