Adds an external network gateway to the specified router

    CLI Example:

    .. code-block:: bash

        salt '*' neutron.add_gateway_router router-name ext-network-name

    :param router: ID or name of the router
    :param ext_network: ID or name of the external network the gateway
    :param profile: Profile to build on (Optional)
    :return: Added Gateway router information

def add_gateway_router(router, ext_network, profile=None):
    '''
    Adds an external network gateway to the specified router

    CLI Example:

    .. code-block:: bash

        salt '*' neutron.add_gateway_router router-name ext-network-name

    :param router: ID or name of the router
    :param ext_network: ID or name of the external network the gateway
    :param profile: Profile to build on (Optional)
    :return: Added Gateway router information
    '''
    conn = _auth(profile)
    return conn.add_gateway_router(router, ext_network)