examples/ipsec-secgw: add poll mode worker for inline proto

examples/ipsec-secgw: add poll mode worker for inline proto

Add separate worker thread when all SA's are of type
inline protocol offload and librte_ipsec is enabled
in order to make it more optimal for that case.
Current default worker supports all kinds of SA leading
to doing lot of per-packet checks and branching based on
SA type which can be of 5 types of SA's.

Also make a provision for choosing different poll mode workers
for different combinations of SA types with default being
existing poll mode worker that supports all kinds of SA's.

Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>