Fixed integer overflow in e1000e

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1737400
Fixed setting max_queue_num if there are no peers in
NICConf. qemu_new_nic() creates NICState with 1 NetClientState(index
0) without peers, set max_queue_num to 0 - It prevents undefined
behavior and possible crashes, especially during pcie hotplug.

Fixes: 6f3fbe4e ("net: Introduce e1000e device emulation")
Signed-off-by: NAndrew Melnychenko <andrew@daynix.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NDmitry Fleytman <dmitry.fleytman@gmail.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>

hw/net/e1000e.c

@@ -328,7 +328,7 @@ e1000e_init_net_peer(E1000EState *s, PCIDevice *pci_dev, uint8_t *macaddr)
     s->nic = qemu_new_nic(&net_e1000e_info, &s->conf,
         object_get_typename(OBJECT(s)), dev->id, s);
 
-    s->core.max_queue_num = s->conf.peers.queues - 1;
+    s->core.max_queue_num = s->conf.peers.queues ? s->conf.peers.queues - 1 : 0;
 
     trace_e1000e_mac_set_permanent(MAC_ARG(macaddr));
     memcpy(s->core.permanent_mac, macaddr, sizeof(s->core.permanent_mac));