MT#62859 AmB2BSession::onB2BEvent send fake SDP answer

In case of INVITE pending UAC transactions for the other leg,
and new coming in (like 200OK send to this leg, and just right
after that re-INVITE), just provide a fake SDP answer (200OK)
in the meanwhile.

And expect that a finished UAC transaction on the other side,
must trigger a consequent update for this leg, what will finish
these media negotiations.

Change-Id: I190dfcd5467c728e2192940dfac8454f708cecaf

core/AmB2BSession.cpp

@@ -327,13 +327,19 @@ void AmB2BSession::onB2BEvent(B2BEvent* ev)
           }
 
           if (req_ev->req.method == SIP_METH_INVITE && dlg->getUACInvTransPending()) {
-            /* don't relay INVITE if INV trans pending */
-            ILOG_DLG(L_DBG, "Not sip-relaying INVITE with pending INV transaction, b2b-relaying 491 pending\n");
-            relayError(req_ev->req.method, req_ev->req.cseq, true, 491, SIP_REPLY_PENDING);
+            ILOG_DLG(L_DBG, "There are still pending UAC INVITE transactions, this leg: '%s' (UAC) -> other leg: '%s'\n",
+                            dlg->getLocalTag().c_str(),
+                            getOtherId().c_str());
+            ILOG_DLG(L_DBG, "Sending a fake 200OK to this transaction in the meanwhile (CSeq: %d)\n", req_ev->req.cseq);
+            /* UAC side (other side) already has a pending update, this one just overrides it?
+            * let the UAC respond, what will trigger a back update again and negotiations should be finished by that
+            */
+            acceptPendingInviteB2B(req_ev->req);
             return;
           }
 
-          if (req_ev->req.method == SIP_METH_BYE && dlg->getStatus() != AmBasicSipDialog::Connected) {
+          if (req_ev->req.method == SIP_METH_BYE &&
+              dlg->getStatus() != AmBasicSipDialog::Connected) {
             ILOG_DLG(L_DBG, "not sip-relaying BYE in not connected dlg, b2b-relaying 200 OK\n");
             relayError(req_ev->req.method, req_ev->req.cseq, true, 200, "OK");
             return;