net/ena: recreate HW IO rings on start and stop

net/ena: recreate HW IO rings on start and stop

On the start the driver was refilling all Rx buffs, but the old ones
were not released. That way running start/stop for a few times was
causing device to run out of descriptors.

To fix the issue, IO rings are now being destroyed on stop, and
recreated on start. That way the device is not losing any descriptors.

Furthermore, there was also memory leak for the Rx mbufs, which were
created on start and not destroyed on stop.

Fixes: eb0ef49dd5d5 ("net/ena: add stop and uninit routines")
Cc: stable@dpdk.org
Signed-off-by: Michal Krawczyk <mk@semihalf.com>