LU-14673 sec: annotate algorithms taking optional key

LU-14673 sec: annotate algorithms taking optional key

Crypto algorithms implementing a ->setkey() method but that can also
be used without a key must set the CRYPTO_ALG_OPTIONAL_KEY flag if
defined in the kernel.
In Lustre, adler32 implementation defines a ->setkey() method, but
its "key" is not actually a cryptographic key.

Linux-commit: a208fa8f33031b9e0aba44c7d1b7e68eb0cbd29e

Lustre-change: https://review.whamcloud.com/43656
Lustre-commit: b161e7b777e63bb4328aeab9e50560f919fedc31

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I362211d1b1aa3763fe1481cebb3629b255f29e41
Reviewed-on: https://review.whamcloud.com/43860
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>