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)
........

Merged revisions 404579 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@404581 f38db490-d61c-443f-a65b-d21fe96a405b