net: fix infinite loop on exit

1ceef9f273 added handling for cleaning
up multiple queues in qemu_del_nic() for cases where multiqueue is in
use. To determine the number of queues it looks at nic->conf->queues,
then iterates through all the queues to cleanup the associated
NetClientStates. If no queues are found, no NetClientStates are deleted.

However, nic->conf->queues is only set when a peer is created via
-netdev or netdev_add, and is otherwise 0. This causes us to spin in
net_cleanup() if we attempt to shut down qemu before adding a host
device.

Since qemu_new_nic() unconditionally creates at least 1
queue/NetClientState at queue idx 0, make qemu_del_nic() always attempt
to clean it up.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

net/net.c

@@ -351,7 +351,7 @@ void qemu_del_net_client(NetClientState *nc)
 
 void qemu_del_nic(NICState *nic)
 {
-    int i, queues = nic->conf->queues;
+    int i, queues = MAX(nic->conf->queues, 1);
 
     /* If this is a peer NIC and peer has already been deleted, free it now. */
     if (nic->peer_deleted) {