MT#55283 ice: avoid forcing ICE in a non-ICE answer without an ICE agent

Closes #2207

Change-Id: I174419dc418f0d2e0b9b05908d6b17dabf6a3d57
(cherry picked from commit 653650d1cc)
(cherry picked from commit a542784f18)

daemon/call.c

@@ -1428,6 +1428,14 @@ static void __ice_offer(const sdp_ng_flags *flags, struct call_media *this,
 	if (flags->ice_reject)
 		MEDIA_CLEAR(other, ICE);
 
+	// An answer must not introduce ICE where the original offer did not
+	// advertise it. A locally created ICE agent means we intentionally
+	// offered ICE on this leg, in which case keep the negotiated state.
+	// In other cases ignore ICE=force on the answer (see issue #2161).
+	if (flags->opmode == OP_ANSWER && flags->ice_option == ICE_FORCE &&
+			!MEDIA_ISSET(other, ICE) && !this->ice_agent)
+		MEDIA_CLEAR(this, ICE);
+
 	if (flags->passthrough_on) {
 		ilog(LOG_DEBUG, "enabling passthrough mode");
 		MEDIA_SET(this, PASSTHRU);