net: purge queued rx packets on queue deletion

https://bugzilla.redhat.com/show_bug.cgi?id=1829272
When deleting queue pair, purge pending RX packets if any.
Example of problematic flow:
1. Bring up q35 VM with tap (vhost off) and virtio-net or e1000e
2. Run ping flood to the VM NIC ( 1 ms interval)
3. Hot unplug the NIC device (device_del)
   During unplug process one or more packets come, the NIC
   can't receive, tap disables read_poll
4. Hot plug the device (device_add) with the same netdev
The tap stays with read_poll disabled and does not receive
any packets anymore (tap_send never triggered)

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/net.c

@@ -412,10 +412,14 @@ void qemu_del_nic(NICState *nic)
 
     qemu_macaddr_set_free(&nic->conf->macaddr);
 
-    /* If this is a peer NIC and peer has already been deleted, free it now. */
-    if (nic->peer_deleted) {
-        for (i = 0; i < queues; i++) {
-            qemu_free_net_client(qemu_get_subqueue(nic, i)->peer);
+    for (i = 0; i < queues; i++) {
+        NetClientState *nc = qemu_get_subqueue(nic, i);
+        /* If this is a peer NIC and peer has already been deleted, free it now. */
+        if (nic->peer_deleted) {
+            qemu_free_net_client(nc->peer);
+        } else if (nc->peer) {
+            /* if there are RX packets pending, complete them */
+            qemu_purge_queued_packets(nc->peer);
         }
     }