Warning for check_items with default config

[qnet-herwin]

Basicly a continuation of http://lists.freeradius.org/pipermail/freeradius-users/2015-October/080219.html

Witht the default configuration, FreeRADIUS generates warnings about the contents of mods-config/attr_filter/access_reject. We've added the items FreeRADIUS-Response-Delay and FreeRADIUS-Response-Delay-USec in #1216, and we're warned about that in https://github.com/FreeRADIUS/freeradius-server/blob/release_3_0_10/src/modules/rlm_attr_filter/rlm_attr_filter.c#L108-L117

Given the comment in https://github.com/FreeRADIUS/freeradius-server/pull/1216#issuecomment-138924345, I'd assume that this check could be removed completely.

[arr2036]

@alandekok maybe we should only raise an issue for user defined attributes i.e. non-internal?

[arr2036]

Ug but 3.0.x doesn't have an internal flag... So I guess just non-vsa attributes > 255