features_config: Fix config ref leak of parkinglots.

This leak happend for just about every channel created.
........

Merged revisions 399585 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399586 65c4cc65-6c06-0410-ace0-fbb531ad65f3