Fix missing 64bit carry handling in AES-NI CTR mode

* cipher/rijndael.c [USE_AESNI] (do_aesni_ctr, do_aesni_ctr_4): Add
carry handling to 64-bit addition.
(selftest_ctr_128): New function for testing IV handling in bulk CTR
function.
(selftest): Add call to selftest_ctr_128.

Carry handling checks if lower 64-bit part of SSE register was overflowed and
if it was, increment upper parts since that point. Also add selftests to verify
correct operation.

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>