examples/ipsec-secgw: make app to use IPsec library

examples/ipsec-secgw: make app to use IPsec library

Changes to make ipsec-secgw to utilize librte_ipsec library.
That patch provides:
 - changes in the related data structures.
 - changes in the initialization code.
 - new command-line parameters to enable librte_ipsec codepath
   and related features.

Note that right now by default current (non-librte_ipsec) code-path will
be used. User has to run application with new command-line option ('-l')
to enable new codepath.
The main reason for that:
 - current librte_ipsec doesn't support all ipsec algorithms
   and features that the app does.
 - allow users to run both versions in parallel for some time
   to figure out any functional or performance degradation with the
   new code.

It is planned to deprecate and remove non-librte_ipsec code path
in future releases.

Signed-off-by: Mohammad Abdul Awal <mohammad.abdul.awal@intel.com>
Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Radu Nicolau <radu.nicolau@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>