Correctly hide the dialpad

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/components/views/voip/CallView.tsx

@@ -534,7 +534,7 @@ export default class CallView extends React.Component<IProps, IState> {
             );
         }
         let dialpadButton;
-        if (this.state.callState === CallState.Connected && CallHandler.sharedInstance().getSupportsPstnProtocol()) {
+        if (this.state.callState === CallState.Connected && this.props.call.opponentSupportsDTMF()) {
             dialpadButton = (
                 <ContextMenuButton
                     className="mx_CallView_callControls_button mx_CallView_callControls_dialpad"