[PATCH] ipt_limit fix for HZ=1000

[PATCH] ipt_limit fix for HZ=1000

The range that the iptables limit extension can specify depends on HZ.
This means that rules which worked i386 2.4 (100 HZ) won't work on
2.6.

The solution is to adjust the precision based on the HZ value (keeping
the range of possible values the same).  For extra geek cred, this is
done by calculating a power-of-two constant below the maximum
multiplication factor, which gcc then turns into a simple shift.