parallel cgd

[mlelstv%serpens.de@localhost (Michael van Elst)]

I have committed a change to cgd(4) that defers crypto operations
to a parallel work queue. This should improve performance on
multi-core systems.

On a system with Core i5-2520 (2.5GHz) with 2 Cores and 2 Threads/Core
I now get 150-180MByte/s reading and writing the raw device. 

For comparison, 'openssl speed -multi 4 aes-128-cbc' returns an aggregated
rate of ~200MByte/s.

Feedback welcome.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."