Ensure iax2 debug output is displayed when expected

When IAX2 debug was changed from iax_showframe to iax_outputframe,
some instances were missed (or added afterward). This was causing
debug output to not be displayed when expected.

(closes issue ASTERISK-20338)
Reported-by: John Covert
Patch-by: John Covert
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Merged revisions 372804 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 372805 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@372806 65c4cc65-6c06-0410-ace0-fbb531ad65f3