Eric Biggers authored Jan 03, 2018 and Herbert Xu committed Jan 12, 2018

Similar to what was done for the hash API, update the skcipher API to
track whether each transform has been keyed, and reject
encryption/decryption if a key is needed but one hasn't been set.

This isn't as important as the equivalent fix for the hash API because
symmetric ciphers almost always require a key (the "null cipher" is the
only exception), so are unlikely to be used without one.  Still,
tracking the key will prevent accidental unkeyed use.  algif_skcipher
also had to track the key anyway, so the new flag replaces that and
simplifies the algif_skcipher implementation.

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