Set the port number of the destination monitor port.
The monitor-port is the port that we can monitor the RMirror traffic:
1. A monitor-port is only in destination switch.
2. It can participate in only one RMirror VLAN at a time.
3. A monitor-port in one RMirror VLAN cannot be another RMirror VLAN.
4. A monitor-port can not be a mirror-port, reflector-port and connected-port.