Patch 1/3

1) No more one rwlock_t protecting the 'curtain'

One major bottleneck on SMP machines is the fact that one rwlock
is taken in ipt_do_table() entry and exit. That 2 atomic operations are
the killer, and even if multiple readers can work together on the same table
(using read_lock_bh()), the cache line containing rwlock still must be
taken exclusively by each CPU at entry/exit of ipt_do_table().

As existing code already use separate copies of the data for each cpu, it is
very easy to convert the central rwlock to separate rwlocks, allocated
percpu (and NUMA aware).

When a cpu enters ipt_do_table(), it can locks its local copy, touching a
cache line that is not used by other cpus. Further operations are done on
'local' copy of the data.

When a sum of all counters must be done, we can write_lock each part at a
time, instead of locking all the parts, reducing the lock contention.

Note1 : I also optimized get_counters(), using a SET_COUNTER() for the first 
cpu, avoiding a memset() and ADD_COUNTER() if SMP on other cpus.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>