totemcrypto: major code cleanup (no functional or onwire changes)

• cleanup include list
• reorder code and functions (crypto then hash)
• split crypt/decrypt/hash functions
• some micro optimizations by dropping a few memcpy
• make the code more readable (better var names and buffers mapping)
• improve exit paths on error (return codes and free)
• store crypto header size instead of recalculating it per packet

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>