Add MP4 to part of the SDP code.

(closes issue #10820)
Reported by: ruikubo
Patches:
      chan_sip.patch uploaded by ruikubo (license 250)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@84165 65c4cc65-6c06-0410-ace0-fbb531ad65f3