test/distributor: fix worker notification in burst mode

test/distributor: fix worker notification in burst mode

Because a single worker can process more than one packet from the
distributor, the final set of notifications in burst mode should be
sent one-by-one to ensure that each worker has a chance to wake up.

This fix mirrors the change done in the functional test by
commit f72bff0ec272 ("test/distributor: fix quitting workers in burst
mode").

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