code: func (sm *ServiceMap) unmerge(other ServiceMap, UDPStaleClusterIP sets.String) {
  	for svcPortName := range other {
  		info, exists := (*sm)[svcPortName]
  		if exists {
  			klog.V(1).Infof("Removing service port %q", svcPortName)
  			if info.GetProtocol() == v1.ProtocolUDP {
  				UDPStaleClusterIP.Insert(info.ClusterIPString())
  			}
  			delete(*sm, svcPortName)
  		} else {
  			klog.Errorf("Service port %q doesn't exists", svcPortName)
  		}
  	}
  }
docs: // unmerge deletes all other ServiceMap's elements from current ServiceMap.  We pass in the UDPStaleClusterIP strings sets
  // for storing the stale udp service cluster IPs. We will clear stale udp connection base on UDPStaleClusterIP later