channels.c: core show channeltypes slicing

'core show channeltypes' type column is being sliced, resulting in incomplete
type names.

(closes issue ASTERISK-22919)
Reported by: outtolunc
Patches:
     svn_channel.c.format_15.diff.txt uploaded by outtolunc (license 5198)
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Merged revisions 404579 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 404581 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@404582 65c4cc65-6c06-0410-ace0-fbb531ad65f3