vport: make client free queue accessed as multiple consumer ring

Fix concurrency issue on client free queue being accessed by
multiple threads in a single-consumer way. Changed access to
multiple-consumer. The concurrency issue may lead to possible memory
corruption.

Change-Id: I44c0f8f43c5d93feef45dcd45bd59c91b6a43dbd
Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>
Signed-off-by: Nicolas Pernas Maradei <nicolasx.pernas.maradei@intel.com>