[spp] Change sec command to nfv

[Yasufumi Ogawa]

Hi all,

Until now, SPP has had four types of secondary process, spp_nfv, spp_vm, spp_vf and spp_mirror, and going to increased in a 
future release. Command name `sec` was defined because there were just two types secondaries and can be managed with one 
command. However, it is not appropriate because spp_vf and spp_mirror are also secondary processes.

I will change the command name from `sec` to `nfv` in the next patches.

Thanks,
Yasufumi

-- 
Yasufumi Ogawa
NTT Network Service Systems Labs