[nsp] IP NAT Ager gobbling CPU

[atticus at satanic.org]

On an NPE-400, I'm burning huge amounts of CPU (~40%) on IP NAT Ager. NAT
is about the only thing the router does, but its currently aging ~225
translations per second, w/ the total active hovering around 15k. All of
the connections are TCP.

There's 252 pools, all of which are used as inside source static
overloads, and the only non-default aging parameter is 'tcp-timeout 60'.

Not being able to find any debug switches for the NAT aging process (only
top-level for ip nat, which doesn't appear to print ager info), I'm hoping
someone can shed some light into whether this is about what to expect, or
if there's any aging knobs that might improve things.

thanks.