[6.1] libvirtd reports a certain error message many times when shutting down all guest OSes configuring with a bridge.

Issue

• When we start virt-manager in the state that all the guest OS's of the bridge (br0) constitution stopped, libvirtd reports a large quantity of error message in a syslog.
• libvirtd reports the following error message to /var/log/messages every second when virt-manager shuts down all guest OSes configuring with a bridge br0.

May 24 10:30:09 hostname1 libvirtd: 10:30:09.707: 1918: error : virInterfaceDefParseXML:744 :  
XML description for bridge interface misses the bridge element is not well formed or invalid  

• But, the above message looks improper and unnecessary because all guest OSes have been shut down normally.