net: Report error when device / hub combo is not found.

Also convert nearby monitor_printf() call to error_report().
Signed-off-by: NHani Benhabiles <hani@linux.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

net/net.c

@@ -952,10 +952,12 @@ void net_host_device_remove(Monitor *mon, const QDict *qdict)
 
     nc = net_hub_find_client_by_name(vlan_id, device);
     if (!nc) {
+        error_report("Host network device '%s' on hub '%d' not found",
+                     device, vlan_id);
         return;
     }
     if (!net_host_check_device(nc->model)) {
-        monitor_printf(mon, "invalid host network device %s\n", device);
+        error_report("invalid host network device '%s'", device);
         return;
     }
     qemu_del_net_client(nc);