chan_iax2: Correct spelling of 'Port' header in IAX2 PeerStatus AMI Events

The PeerStatus event for IAX2 channels currently includes a header named Post
which should have been Port.  Post was removed and the AMI version has been
updated to 1.3.
........

Merged revisions 359982 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@359983 65c4cc65-6c06-0410-ace0-fbb531ad65f3