ring: introduce staged ordered ring

Staged-Ordered-Ring (SORING) provides a SW abstraction for 'ordered' queues
with multiple processing 'stages'.
It is based on conventional DPDK rte_ring, re-uses

ring: introduce staged ordered ring

Staged-Ordered-Ring (SORING) provides a SW abstraction for 'ordered' queues
with multiple processing 'stages'.
It is based on conventional DPDK rte_ring, re-uses many of its concepts,
and even substantial part of its code.
It can be viewed as an 'extension' of rte_ring functionality.
In particular, main SORING properties:
- circular ring buffer with fixed size objects
- producer, consumer plus multiple processing stages in the middle.
- allows to split objects processing into multiple stages.
- objects remain in the same ring while moving from one stage to the other,
initial order is preserved, no extra copying needed.
- preserves the ingress order of objects within the queue across multiple
stages, i.e.:
at the same stage multiple threads can process objects from the ring in
any order, but for the next stage objects will always appear in the
original order.
- each stage (and producer/consumer) can be served by single and/or
multiple threads.
- number of stages, size and number of objects in the ring are
configurable at ring initialization time.

Data-path API provides four main operations:
- enqueue/dequeue works in the same manner as for conventional rte_ring,
all rte_ring synchronization types are supported.
- acquire/release - for each stage there is an acquire (start) and
release (finish) operation.
after some objects are 'acquired' - given thread can safely assume that
it has exclusive possession of these objects till 'release' for them is
invoked.
Note that right now user has to release exactly the same number of
objects that was acquired before.
After 'release', objects can be 'acquired' by next stage and/or dequeued
by the consumer (in case of last stage).

Expected use-case: applications that uses pipeline model
(probably with multiple stages) for packet processing, when preserving
incoming packet order is important. I.E.: IPsec processing, etc.

Signed-off-by: Eimear Morrissey <eimear.morrissey@huawei.com>
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>

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