networking-spp has not been able to upgrade DPDK/SPP version from
v18.08 because DPDK v18.11 and later have a problem that secondary
processes can not use vhost PMD.
Now the problem is fixed in DPDK v20.02, this patch makes Neutron
SPP driver use DPDK/SPP v20.02.
Change-Id: Ic51071c10bf8f7b954586c82bbf85421918be55e
Blueprint: upgrade-dpdk-2002
b0a66719b9