rtpengine: fix offer vs answer detection for replies

When late negociation is not used, rtpengine_manage() should send an
answer command, not an offer one.

(cherry picked from commit d064131)

modules/rtpengine/doc/rtpengine_admin.xml

@@ -738,13 +738,6 @@ rtpengine_delete();
 			If INVITE with SDP, then do <function>rtpengine_offer()</function>
 			</para>
 		</listitem>
-		<listitem>
-			<para>
-			If INVITE with SDP, when the tm module is loaded, mark transaction with
-			internal flag FL_SDP_BODY to know that the 1xx and 2xx are for
-			<function>rtpengine_answer()</function>
-			</para>
-		</listitem>
 		<listitem>
 			<para>
 			If ACK with SDP, then do <function>rtpengine_answer()</function>

modules/rtpengine/rtpengine.c

@@ -2393,6 +2393,9 @@ rtpengine_manage(struct sip_msg *msg, const char *flags, pv_spec_t *spvar, pv_sp
 {
 	int method;
 	int nosdp;
+	int op = OP_ANSWER;
+	struct cell *t;
+	struct sip_msg req;
 
 	if(msg->cseq==NULL && ((parse_headers(msg, HDR_CSEQ_F, 0)==-1)
 				|| (msg->cseq==NULL)))
@@ -2431,10 +2434,19 @@ rtpengine_manage(struct sip_msg *msg, const char *flags, pv_spec_t *spvar, pv_sp
 		if(nosdp==0) {
 			if(method==METHOD_UPDATE)
 				return rtpengine_offer_answer(msg, flags, spvar, bpvar, OP_ANSWER);
-			if(tmb.t_gett==NULL || tmb.t_gett()==NULL
-					|| tmb.t_gett()==T_UNDEFINED)
-				return rtpengine_offer_answer(msg, flags, spvar, bpvar, OP_ANSWER);
-			return rtpengine_offer_answer(msg, flags, spvar, bpvar, OP_OFFER);
+			if (tmb.t_gett != NULL) {
+				t = tmb.t_gett();
+				if(t && t != T_UNDEFINED) {
+					/* dup the request so that we don't overlap with other
+					 * replies that might parse the request in the same time */
+					req = *t->uas.request;
+					if (!msg_has_sdp(&req))
+						op = OP_OFFER;
+					free_sip_body(req.body);
+				}
+			}
+			/* op defaults to OP_ANSWER */
+			return rtpengine_offer_answer(msg, flags, spvar, bpvar, op);
 		}
 	}
 	return -1;