net/http: clarify that MaxBytesReader returns *MaxBytesError

A MaxBytesReader returns a *MaxBytesError when reading beyond
its limit, not a MaxBytesError.

Fixes #53764.

Change-Id: Icac3aeac96fd8b172f951241f8f111cda633752c
Reviewed-on: https://go-review.googlesource.com/c/go/+/416914
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/net/http/request.go

diff --git a/src/net/http/request.go b/src/net/http/request.go
index d091f3c..cead91d 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -1126,8 +1126,8 @@
 // MaxBytesReader is similar to io.LimitReader but is intended for
 // limiting the size of incoming request bodies. In contrast to
 // io.LimitReader, MaxBytesReader's result is a ReadCloser, returns a
-// MaxBytesError for a Read beyond the limit, and closes the
-// underlying reader when its Close method is called.
+// non-nil error of type *MaxBytesError for a Read beyond the limit,
+// and closes the underlying reader when its Close method is called.
 //
 // MaxBytesReader prevents clients from accidentally or maliciously
 // sending a large request and wasting server resources. If possible,