Improve consistency of party ID privacy usage.

Improve consistency of party ID privacy usage.

Prior to this change, the Remote-Party-ID header took the position of
"If caller name and number are not explicitly allowed, then they are private"
and P-Asserted-Identity took the position of
"Caller name and number are only private if marked explicitly so"

Now both mechanisms of conveying party identification use the former approach.
........

Merged revisions 421778 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@421783 65c4cc65-6c06-0410-ace0-fbb531ad65f3