examples/ipsec-secgw: add driver mode worker

examples/ipsec-secgw: add driver mode worker

Add driver inbound and outbound worker thread for ipsec-secgw. In driver
mode application does as little as possible. It simply forwards packets
back to port from which traffic was received instructing HW to apply
inline security processing using first outbound SA configured for
a given port. If a port does not have SA configured outbound traffic
on that port will be silently dropped. The aim of this mode is to
measure HW capabilities. Driver mode is selected with single-sa option.
The single-sa option accepts SA index however in event mode the SA
index is ignored.

Example command to run ipsec-secgw in driver mode:
ipsec-secgw -w 0002:02:00.0,ipsec_in_max_spi=128
-w 0002:03:00.0,ipsec_in_max_spi=128 -w 0002:0e:00.0 -w 0002:10:00.1
--log-level=8 -c 0x1 -- -P -p 0x3 -u 0x1 -f aes-gcm.cfg
--transfer-mode event --event-schedule-type parallel --single-sa 0

Signed-off-by: Anoob Joseph <anoobj@marvell.com>
Signed-off-by: Ankur Dwivedi <adwivedi@marvell.com>
Signed-off-by: Lukasz Bartosik <lbartosik@marvell.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>