rtp_engine: Output mixup in ${CHANNEL(rtpqos,audio,all)}

rtp_engine: Output mixup in ${CHANNEL(rtpqos,audio,all)}

Fixed the output of CHANNEL(rtpqos,audio,all) to use txjitter instead
of rxjitter.

(closes issue ASTERISK-23261)
Reported by: rsw686
Patches:
     rtpqos.patch uploaded by rsw686 (license 5887)
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Merged revisions 408646 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 408647 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 408649 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@408652 65c4cc65-6c06-0410-ace0-fbb531ad65f3