Create and initialize udptl only when dialog negotiates for image media

Create and initialize udptl only when dialog negotiates for image media

Prior to this patch, the udptl struct was allocated and initialized when a
dialog was associated with a peer that supported T.38, when a new SIP
channel was allocated, or what an INVITE request was received.  This resulted
in any dialog associated with a peer that supported T.38 having udptl support
assigned to it, including the UDP ports needed for communication.  This
occurred even in non-INVITE dialogs that would never send image media.

This patch creates and initializes the udptl structure only when the SDP
for a dialog specifies that image media is supported, or when Asterisk
indicates through the appropriate control frame that a dialog is to support
T.38.

(closes issue ASTERISK-16698)
Reported by: under
Tested by: Stefan Schmidt
Patches: udptl_20120113.diff uploaded by mjordan (License #6283)

(closes issue ASTERISK-16794)
Reported by: Elazar Broad
Tested by: Stefan Schmidt

review: https://reviewboard.asterisk.org/r/1668/
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Merged revisions 351027 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 351028 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@351029 65c4cc65-6c06-0410-ace0-fbb531ad65f3