code: public static synchronized ModbusSlave getSlave(AbstractModbusListener listener) {
          for (ModbusSlave slave : slaves.values()) {
              if (slave.getListener().equals(listener)) {
                  return slave;
              }
          }
          return null;
      }
docs: Returns the running slave that utilises the give listener
  
  @param listener Listener used for this slave
  @return Null or ModbusSlave