Add autocompletion to "iax2 set debug peer".

(closes issue #13129)
Reported by: eliel
Patches:
      chan_iax2.c.patch uploaded by eliel (license 64)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@132572 65c4cc65-6c06-0410-ace0-fbb531ad65f3