chan_sip: Trigger reinvite if the SDP answer is included in the SIP ACK

Under certain conditions, a SIP transaction involving directmedia wouldn't
trigger a re-invite because the SDP answer was included in an ACK instead
of in a message that we would have triggered the invite with. This patch
just queues a source change control frame if the dialog is using
directmedia when we find sdp for an ACK.

(closes issue AST-913)
Reported by: Thomas Arimont
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Merged revisions 371337 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371338 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 371355 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371356 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -27376,9 +27376,13 @@ static int handle_incoming(struct sip_pvt *p, struct sip_request *req, struct as
 			p->pendinginvite = 0;
 			acked = __sip_ack(p, seqno, 1 /* response */, 0);
 			if (find_sdp(req)) {
-				if (process_sdp(p, req, SDP_T38_NONE))
+				if (process_sdp(p, req, SDP_T38_NONE)) {
 					return -1;
 				}
+				if (ast_test_flag(&p->flags[0], SIP_DIRECT_MEDIA)) {
+					ast_queue_control(p->owner, AST_CONTROL_SRCCHANGE);
+				}
+			}
 			check_pendings(p);
 		} else if (p->glareinvite == seqno) {
 			/* handle ack for the 491 pending sent for glareinvite */