SIP Show channelstats fix - use float division to show proper stats

(closes issue #15819)
Reported by: klaus3000
Patches: 
      asterisk-sip-show-channelstats-trunk.txt uploaded by klaus3000 (license 65)
Tested by: klaus3000, oej

This patch is for trunk only and will be blocked in 1.6.2



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@239663 65c4cc65-6c06-0410-ace0-fbb531ad65f3