ACTION-84: Wiley to describe the reason for setting DNT=null

Description:
Wiley to describe the reason for setting DNT=null

Draft:
<non-normative>
As many User Agents may fall outside of the large web browser vendors, such as Apps, Toolbars, Custom Web Kits, etc., it will be helpful for publishers to receive a signal that a User Agent supports DNT even when a user has not yet provided a preference.

<normative>
User Agents SHOULD provide a null DNT signal if the user has not yet provided a preference and the User Agent supports DNT.