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)


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@404579 f38db490-d61c-443f-a65b-d21fe96a405b