We were computing the next IV in software instead of reading it from HW
on the premise that this can be quicker due to the small size of IVs but
this proved to be much more hassle and bug ridden than expected.

Move to reading the next IV as computed by the HW.

This fixes a number of issue with next IV being wrong for OFB, CTS-CBC
and probably most of the other ciphers as well.
Signed-off-by: NGilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>