When configuring the adaptive jitterbuffer, the target_extra
value not only could not be set from the configuration, but was
not even being set to its proper default.  This value is required
in order for the adaptive jitterbuffer to work correctly.  To resolve
this a config option has been added to expose this value to the conf
files, and a default value is provided when no config specific value
is present.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@249893 65c4cc65-6c06-0410-ace0-fbb531ad65f3