Set tagging of native VLAN on trunk.

        Args:
            int_type (str): Type of interface. (gigabitethernet,
                tengigabitethernet, etc)
            name (str): Name of interface. (1/0/5, 1/0/10, etc)
            mode (str): Trunk port mode (trunk, trunk-no-default-native).
            enabled (bool): Is tagging of the VLAN enabled on trunks?
                (True, False)
            callback (function): A function executed upon completion oj the
                method.  The only parameter passed to `callback` will be the
                ``ElementTree`` `config`.

        Returns:
            Return value of `callback`.

        Raises:
            KeyError: if `int_type`, `name`, or `state` is not specified.
            ValueError: if `int_type`, `name`, or `state` is not valid.

        Examples:
            >>> import pynos.device
            >>> switches = ['10.24.39.211', '10.24.39.203']
            >>> auth = ('admin', 'password')
            >>> for switch in switches:
            ...     conn = (switch, '22')
            ...     with pynos.device.Device(conn=conn, auth=auth) as dev:
            ...         output = dev.interface.trunk_mode(
            ...         int_type='tengigabitethernet',
            ...         name='225/0/38', mode='trunk')
            ...         output = dev.interface.tag_native_vlan(name='225/0/38',
            ...         int_type='tengigabitethernet')
            ...         output = dev.interface.tag_native_vlan(
            ...         int_type='tengigabitethernet',
            ...         name='225/0/38', enabled=False)
            ...         dev.interface.tag_native_vlan()
            ...         # doctest: +IGNORE_EXCEPTION_DETAIL
            Traceback (most recent call last):
            KeyError

def tag_native_vlan(self, **kwargs):
        """Set tagging of native VLAN on trunk.

        Args:
            int_type (str): Type of interface. (gigabitethernet,
                tengigabitethernet, etc)
            name (str): Name of interface. (1/0/5, 1/0/10, etc)
            mode (str): Trunk port mode (trunk, trunk-no-default-native).
            enabled (bool): Is tagging of the VLAN enabled on trunks?
                (True, False)
            callback (function): A function executed upon completion oj the
                method.  The only parameter passed to `callback` will be the
                ``ElementTree`` `config`.

        Returns:
            Return value of `callback`.

        Raises:
            KeyError: if `int_type`, `name`, or `state` is not specified.
            ValueError: if `int_type`, `name`, or `state` is not valid.

        Examples:
            >>> import pynos.device
            >>> switches = ['10.24.39.211', '10.24.39.203']
            >>> auth = ('admin', 'password')
            >>> for switch in switches:
            ...     conn = (switch, '22')
            ...     with pynos.device.Device(conn=conn, auth=auth) as dev:
            ...         output = dev.interface.trunk_mode(
            ...         int_type='tengigabitethernet',
            ...         name='225/0/38', mode='trunk')
            ...         output = dev.interface.tag_native_vlan(name='225/0/38',
            ...         int_type='tengigabitethernet')
            ...         output = dev.interface.tag_native_vlan(
            ...         int_type='tengigabitethernet',
            ...         name='225/0/38', enabled=False)
            ...         dev.interface.tag_native_vlan()
            ...         # doctest: +IGNORE_EXCEPTION_DETAIL
            Traceback (most recent call last):
            KeyError
        """
        int_type = kwargs.pop('int_type').lower()
        name = kwargs.pop('name')
        enabled = kwargs.pop('enabled', True)
        callback = kwargs.pop('callback', self._callback)

        int_types = ['gigabitethernet', 'tengigabitethernet',
                     'fortygigabitethernet', 'hundredgigabitethernet',
                     'port_channel']

        if int_type not in int_types:
            raise ValueError("Incorrect int_type value.")

        if not pynos.utilities.valid_interface(int_type, name):
            raise ValueError('`name` must be in the format of x/y/z for '
                             'physical interfaces or x for port channel.')

        if not isinstance(enabled, bool):
            raise ValueError("Invalid state.")

        tag_args = dict(name=name)
        tag_native_vlan = getattr(self._interface, 'interface_%s_switchport_'
                                  'trunk_tag_native_vlan' % int_type)
        config = tag_native_vlan(**tag_args)
        if not enabled:
            untag = config.find('.//*native-vlan')
            untag.set('operation', 'delete')

        try:
            return callback(config)
        # TODO: Catch existing 'no switchport tag native-vlan'
        except AttributeError:
            return None