net/virtio: fix memory leak in mergeable packed Rx

When there is no enough segments for a packet in mergeable
packed Rx path, we should free the whole mbuf chain instead
of just recycling the last segment.

Fixes: a76290c8f1 ("net/virtio: implement Rx path for packed queues")
Cc: stable@dpdk.org

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>

drivers/net/virtio/virtio_rxtx.c

@@ -1909,7 +1909,7 @@ virtio_recv_mergeable_pkts_packed(void *rx_queue,
 		} else {
 			PMD_RX_LOG(ERR,
 					"No enough segments for packet.");
-			virtio_discard_rxbuf(vq, prev);
+			rte_pktmbuf_free(rx_pkts[nb_rx]);
 			rxvq->stats.errors++;
 			break;
 		}