lookup the validation function for a [addrfam][attr] and
    return the results

    :param attr: attribute name
    :param value: raw setting value
    :param addrfam: address family (inet, inet6,

def _validate_interface_option(attr, value, addrfam='inet'):
    '''lookup the validation function for a [addrfam][attr] and
    return the results

    :param attr: attribute name
    :param value: raw setting value
    :param addrfam: address family (inet, inet6,
    '''
    valid, _value, errmsg = False, value, 'Unknown validator'
    attrmaps = ATTRMAPS.get(addrfam, [])
    for attrmap in attrmaps:
        if attr in attrmap:
            validate_func = attrmap[attr]
            (valid, _value, errmsg) = validate_func(value)
            break
    return (valid, _value, errmsg)