add one example of DPI ?

[fengchengwen]

Hi all,

Currently, we supported several DPI application scenarios performance tuning,
in these scenarios, the DPDK library ethdev, ring, mbuf and hash APIs are used.

One of the scenarios is:

    ------------------------                           -------------------------
    |                      |       rte_ring-0          |                       |
    |  packet-recv-process | ===>  rte_ring-1  ===>    | packet-detect-process |
    |                      |         ...               |                       |
    |                      |       rte_ring-n          |                       |
    ------------------------                           -------------------------

    packet-recv-process dispatch flow to different rings by such 'rte_hash_crc' 
function.
    packet-detect-process build flow context based on rte_hash library.

I think it is necessary to add a DPI example to show that DPDK has the basic
capability of building DPI applications and provides best performance practices.

Hope to listen to the community's opinions.

Thanks