'get existing info'

def get_existing(self):

    self.existing['interface'] = self.interface
    self.existing['ipv4addr'] = self.intf_info['am4CfgAddr']
    self.existing['ipv6addr'] = self.intf_info['am6CfgAddr']
    self.existing['ipv6enalbe'] = self.intf_info['enableFlag']
