ipfw: Add per-cpu table support.

ipfw: Add per-cpu table support.

This is intended to improve performance and reduce latency for
matching discrete addresses.  Table itself is radix tree.

For exmaple, nginx, 1KB web object, 30K concurrent connections,
1 request/connection.  ipfw is running on the server side.

Comparison between no-match rules and no-match table entries:

                   |  perf-avg | lat-avg | lat-stdev | lat-99%
                   |   (tps)   |  (ms)   |   (ms)    |  (ms)
-------------------+-----------+---------+-----------+---------
100 nomatch rules  | 184752.65 |   67.50 |      5.69 |   79.11
-------------------+-----------+---------+-----------+---------
100 nomatch tblent | 200754.53 |   61.18 |      5.72 |   73.10

1K nomatch rules   |  90836.43 |  144.72 |     12.28 |  168.97
-------------------+-----------+---------+-----------+---------
1K nomatch tblent  | 199750.35 |   61.54 |      5.73 |   72.90

10K nomatch rules  |  14836.69 |  864.46 |    157.49 | 1110.00
-------------------+-----------+---------+-----------+---------
10K nomatch tblent | 198412.93 |   62.17 |      5.66 |   73.08

Comparison between number of no-match table entries:

                   |  perf-avg | lat-avg | lat-stdev | lat-99%
                   |   (tps)   |  (ms)   |   (ms)    |  (ms)
-------------------+-----------+---------+-----------+---------
no-ipfw            | 210658.80 |   58.01 |      5.20 |   68.73
-------------------+-----------+---------+-----------+---------
100 nomatch tblent | 200754.53 |   61.18 |      5.72 |   73.10
-------------------+-----------+---------+-----------+---------
1K nomatch tblent  | 199750.35 |   61.54 |      5.73 |   72.90
-------------------+-----------+---------+-----------+---------
10K nomatch tblent | 198412.93 |   62.17 |      5.66 |   73.08

It scales pretty well with the number of no-match table entries.
En if it is compared w/ no-ipfw case, the performance and latency
impacts of the ipfw after this commit are pretty small.