Set data channel in state.

src/widgets/call-panel.jsx

@@ -309,7 +309,7 @@ class CallPanel extends React.PureComponent {
     channel.onopen = this.handleDataChannelOpen;
     channel.onclose = this.handleDataChannelClose;
 
-    this.setState({pc: pc, waitingForPeer: false});
+    this.setState({pc: pc, dataChannel: channel, waitingForPeer: false});
 
     return pc;
   }

umd/index.dev.js

@@ -10950,6 +10950,7 @@ class CallPanel extends (react__WEBPACK_IMPORTED_MODULE_0___default().PureCompon
     channel.onclose = this.handleDataChannelClose;
     this.setState({
       pc: pc,
+      dataChannel: channel,
       waitingForPeer: false
     });
     return pc;