[PATCH] Adding sysctl for errors statistics to ahd(4)

This patch introduces some mechanisms for collecting informations on
errors frequency and debugging (and relative sysctls for printing them
out) for the ahd(4) driver:
http://www.freebsd.org/~attilio/Sandvine/STABLE_8/ahd/ahd-current2.diff

The usage of array for sysctls is a bit too paranoid but it allows for
further extendibility of the code and doesn't loose of cleaness.
This code has been contributed back by Sandvine Incorporated with some cleanups.
Please review.

Thanks,
Attilio


-- 
Peace can only be achieved by understanding - A. Einstein