Fix the force TURN option

Option needed to be passed in when creating a webrtc call, but for
incoming calls the js-sdk creates the call itself, so the app never
gets a chance to set the option.

src/client.js

@@ -175,6 +175,8 @@ function MatrixClient(opts) {
     this._cryptoStore = opts.cryptoStore;
     this._sessionStore = opts.sessionStore;
 
+    this._forceTURN = opts.forceTURN || false;
+
     if (CRYPTO_ENABLED) {
         this.olmVersion = Crypto.getOlmVersion();
     }
@@ -252,6 +254,15 @@ MatrixClient.prototype.supportsVoip = function() {
     return this._supportsVoip;
 };
 
+/**
+ * Set whether VoIP calls are forced to use only TURN
+ * candidates. This is the same as the forceTURN option
+ * when creating the client.
+ */
+MatrixClient.prototype.setForceTURN = function(forceTURN) {
+    return this._forceTURN = forceTURN;
+};
+
 /**
  * Get the current sync state.
  * @return {?string} the sync state, which may be null.
@@ -3153,7 +3164,9 @@ function setupCallEventHandler(client) {
                 );
             }
 
-            call = webRtcCall.createNewMatrixCall(client, event.getRoomId());
+            call = webRtcCall.createNewMatrixCall(client, event.getRoomId(), {
+                forceTURN: client._forceTURN,
+            });
             if (!call) {
                 console.log(
                     "Incoming call ID " + content.call_id + " but this client " +