Improve our handling of T38 in the initial INVITE from a device.

Improve our handling of T38 in the initial INVITE from a device.

We now answer with matching media streams to what is requested. If an INVITE
is received with both a T38 and RTP media stream this means we answer with both.
For any outgoing calls created as a result of this inbound one no T38 is requested
in the initial INVITE. Instead if we start receiving udptl packets we trigger a
reinvite on the outbound side.

(closes issue #12437)
Reported by: marsosa
Tested by: pinga-fogo, okrief, file, afu

Review: http://reviewboard.digium.com/r/208/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@184947 65c4cc65-6c06-0410-ace0-fbb531ad65f3