Allow skcipher test vectors to declare the value the IV buffer should be
updated to at the end of the encryption or decryption operation.

(This check actually used to be supported in testmgr, but it was never
used and therefore got removed except for the AES-Keywrap special case.
But it will be used by CBC and CTR now, so re-add it.)
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>