chore(doc): Fix outdated limit in comment (#2297)

* fix outdated limit in comment

This mention was missed when the default changed in #1335

* Add backquotes

Co-authored-by: tottoto <tottotodev@gmail.com>

---------

Co-authored-by: tottoto <tottotodev@gmail.com>

Author: darrasse

tonic/src/client/grpc.rs

@@ -181,7 +181,7 @@ impl<T> Grpc<T> {
     ///     .await
     ///     .unwrap();
     ///
-    /// // Set the limit to 2MB, Defaults to 4MB.
+    /// // Set the limit to 2MB, Defaults to `usize::MAX`.
     /// let limit = 2 * 1024 * 1024;
     /// let client = TestClient::new(channel).max_encoding_message_size(limit);
     /// # };