distributor: handle worker shutdown in burst mode

distributor: handle worker shutdown in burst mode

The burst version of distributor implementation was missing proper
handling of worker shutdown. A worker processing packets received
from distributor can call rte_distributor_return_pkt() function
informing distributor that it want no more packets. Further calls to
rte_distributor_request_pkt() or rte_distributor_get_pkt() however
should inform distributor that new packets are requested again.

Lack of the proper implementation has caused that even after worker
informed about returning last packets, new packets were still sent
from distributor causing deadlocks as no one could get them on worker
side.

This patch adds handling shutdown of the worker in following way:
1) It fixes usage of RTE_DISTRIB_VALID_BUF handshake flag. This flag
was formerly unused in burst implementation and now it is used
for marking valid packets in retptr64 replacing invalid use
of RTE_DISTRIB_RETURN_BUF flag.
2) Uses RTE_DISTRIB_RETURN_BUF as a worker to distributor handshake
in retptr64 to indicate that worker has shutdown.
3) Worker that shuts down blocks also bufptr for itself with
RTE_DISTRIB_RETURN_BUF flag allowing distributor to retrieve any
in flight packets.
4) When distributor receives information about shutdown of a worker,
it: marks worker as not active; retrieves any in flight and backlog
packets and process them to different workers; unlocks bufptr64
by clearing RTE_DISTRIB_RETURN_BUF flag and allowing use in
the future if worker requests any new packets.
5) Do not allow to: send or add to backlog any packets for not
active workers. Such workers are also ignored if matched.
6) Adjust calls to handle_returns() and tags matching procedure
to react for possible activation deactivation of workers.

Fixes: 775003ad2f96 ("distributor: add new burst-capable library")
Cc: stable@dpdk.org
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Acked-by: David Hunt <david.hunt@intel.com>