Switch logger callid's from AO2 objects to simple integers.
This helps in two ways.  Copying integers is faster than
referencing AO2 objects, so this will result in a small
reduction in logger overhead.  This also erases the possibility
of an infinate loop caused by an invalid callid in
threadstorage.

ASTERISK-24833 #comment Committed callid conversion to trunk. 
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/4466/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@432834 65c4cc65-6c06-0410-ace0-fbb531ad65f3