>=v144 - update decryption process (AES256_CBC)

[Banaanhangwagen]

With this PR we make firepwd compatible with AES256_CBC decryption as implemented since v144.

However, I had to make a choice here since it's just a quick patch and not a complete rewrite. The stay compatible with older versions, I chose to check for the masterkey length (in stead of algo_oid) and depending on that, picking the right decryption scheme.