[RFC] Macro to sum DPCPU vars

Does anyone have objections to or feedback on the following patch? The 
macro simplifies the act of calculating an aggregate from DPCPU counters.

http://people.freebsd.org/~lstewart/patches/tcp_ffcaia2008/dpcpu_sum_9.x.r208900.patch

If anyone is curious how you would use it, take a look at:

http://people.freebsd.org/~lstewart/patches/tcp_ffcaia2008/siftr_9.x.r208900_v2.patch

and search for code that references the "siftr_stats" struct or "DPCPU".

I intend to commit the DPCPU patch in the next day or two.

Cheers,
Lawrence