net: vmxnet: initialise local tx descriptor

In Vmxnet3 device emulator while processing transmit(tx) queue,
when it reaches end of packet, it calls vmxnet3_complete_packet.
In that local 'txcq_descr' object is not initialised, which could
leak host memory bytes a guest.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/vmxnet3.c

@@ -531,6 +531,7 @@ static void vmxnet3_complete_packet(VMXNET3State *s, int qidx, uint32_t tx_ridx)
 
     VMXNET3_RING_DUMP(VMW_RIPRN, "TXC", qidx, &s->txq_descr[qidx].comp_ring);
 
+    memset(&txcq_descr, 0, sizeof(txcq_descr));
     txcq_descr.txdIdx = tx_ridx;
     txcq_descr.gen = vmxnet3_ring_curr_gen(&s->txq_descr[qidx].comp_ring);