This patch makes the IV generators use the new RNG interface so
that the user can pick an RNG other than the default get_random_bytes.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

This patch adds support for using seqiv with AEAD algorithms.  This is
useful for those AEAD algorithms that performs authentication before
encryption because the IV generated by the underlying encryption algorithm
won't be available for authentication.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

This generator generates an IV based on a sequence number by xoring it
with a salt.  This algorithm is mainly useful for CTR and similar modes.

This patch also sets it as the default IV generator for ctr.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>