ng_ipacct locking rework

[Vsevolod Stakhov]

Hello,

I've reworked the locking model of the ng_ipacct module 
(ports/net-mgmt/ng_ipacct) for better parallel access support. I did the 
following:

- convert locking from a global mutex to hash bucket level locks;
- convert a mutex to rmlock (as ip accounting data is mostly read from 
the hash from my observations).

I appreciate if somebody could review/test this patch and thus I can 
commit it to the port afterwards.

The patches themselves are here:
http://highsecure.ru/patch-ng_ipacct.c
http://highsecure.ru/patch-ng_ipacct_hash.h

Or for comfortable viewing are mirrored on gist:
https://gist.github.com/vstakhov/6223170

-- 
Vsevolod Stakhov