Use backticks not vertical bars to denote variables in comments for /api

Bug: webrtc:12338
Change-Id: Ib97b2c3d64dbd895f261ffa76a2e885bd934a87f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226940
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34554}

api/turn_customizer.h

@@ -29,7 +29,7 @@ class TurnCustomizer {
       cricket::StunMessage* message) = 0;
 
   // TURN can send data using channel data messages or Send indication.
-  // This method should return false if |data| should be sent using
+  // This method should return false if `data` should be sent using
   // a Send indication instead of a ChannelData message, even if a
   // channel is bound.
   virtual bool AllowChannelData(cricket::PortInterface* port,