net/ena: flush Rx buffers memory pool cache

net/ena: flush Rx buffers memory pool cache

As the refill called as part of ena_start(), we end up the refill
progress with stuck buffers at the caller core cache.

Calling to flush the cache results with invalidate this cache and free
those stuck buffers.

Fixes: 1173fca25af9 ("ena: add polling-mode driver")
Cc: stable@dpdk.org
Signed-off-by: Ido Segev <idose@amazon.com>
Reviewed-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Igor Chauskin <igorch@amazon.com>