ipsec: add inbound SAD API

ipsec: add inbound SAD API

According to RFC 4301 IPSec implementation needs an inbound SA database
(SAD).
For each incoming inbound IPSec-protected packet (ESP or AH) it has to
perform a lookup within it's SAD.
Lookup should be performed by:
Security Parameters Index (SPI) + destination IP (DIP) + source IP (SIP)
or SPI + DIP
or SPI only
and an implementation has to return the 'longest' existing match.
This patch extend DPDK IPsec library with inbound security association
database (SAD) API implementation that:
- conforms to the RFC requirements above
- can scale up to millions of entries
- supports fast lookups
- supports incremental updates

Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>