docs: def guest_create_nic(self, userid, vdev=None, nic_id=None,
                           mac_addr=None, active=False):
          """ Create the nic for the vm, add NICDEF record into the user direct.
  
          :param str userid: the user id of the vm
          :param str vdev: nic device number, 1- to 4- hexadecimal digits
          :param str nic_id: nic identifier
          :param str mac_addr: mac address, it is only be used when changing
                 the guest's user direct. Format should be xx:xx:xx:xx:xx:xx,
                 and x is a hexadecimal digit
          :param bool active: whether add a nic on active guest system
  
          :returns: nic device number, 1- to 4- hexadecimal digits
          :rtype: str
          """
          if mac_addr is not None:
              if not zvmutils.valid_mac_addr(mac_addr):
                  raise exception.SDKInvalidInputFormat(
                      msg=("Invalid mac address, format should be "
                           "xx:xx:xx:xx:xx:xx, and x is a hexadecimal digit"))
          return self._networkops.create_nic(userid, vdev=vdev, nic_id=nic_id,
                                             mac_addr=mac_addr, active=active)