test/distributor: fix shutdown of busy worker

test/distributor: fix shutdown of busy worker

The sanity test with worker shutdown delegates all bufs
to be processed by a single lcore worker, then it freezes
one of the lcore workers and continues to send more bufs.
The freezed core shuts down first by calling
rte_distributor_return_pkt().

The test intention is to verify if packets assigned to
the shut down lcore will be reassigned to another worker.

However the shutdown core was not always the one, that was
processing packets. The lcore processing mbufs might be different
every time test is launched. This is caused by keeping the value
of wkr static variable in rte_distributor_process() function
between running test cases.

Test freezed always lcore with 0 id. The patch stores the id
of worker that is processing the data in zero_idx global atomic
variable. This way the freezed lcore is always the proper one.

Fixes: c3eabff124e6 ("distributor: add unit tests")
Cc: stable@dpdk.org
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Tested-by: David Hunt <david.hunt@intel.com>