test/distributor: fix freeing mbufs

test/distributor: fix freeing mbufs

Sanity tests with mbuf alloc and shutdown tests assume that
mbufs passed to worker cores are freed in handlers.
Such packets should not be returned to the distributor's main
core. The only packets that should be returned are the packets
send after completion of the tests in quit_workers function.

This patch stops returning mbufs to distributor's core.
In case of shutdown tests it is impossible to determine
how worker and distributor threads would synchronize.
Packets used by tests should be freed and packets used during
quit_workers() shouldn't. That's why returning mbufs to mempool
is moved to test procedure run on distributor thread
from worker threads.

Additionally this patch cleans up unused variables.

Fixes: c0de0eb82e40 ("distributor: switch over to new API")
Cc: stable@dpdk.org
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Acked-by: David Hunt <david.hunt@intel.com>