net/http: expand documentation of Server.MaxHeaderBytes

Clarify that it includes the RFC 7230 "request-line".

Fixes #15494

Change-Id: I9cc5dd5f2d85ebf903229539208cec4da5c38d04
Reviewed-on: https://go-review.googlesource.com/22656Reviewed-by: Andrew Gerrand <adg@golang.org>

src/net/http/server.go

@@ -2031,12 +2031,18 @@ func Serve(l net.Listener, handler Handler) error {
 // A Server defines parameters for running an HTTP server.
 // The zero value for Server is a valid configuration.
 type Server struct {
-	Addr           string        // TCP address to listen on, ":http" if empty
-	Handler        Handler       // handler to invoke, http.DefaultServeMux if nil
-	ReadTimeout    time.Duration // maximum duration before timing out read of the request
-	WriteTimeout   time.Duration // maximum duration before timing out write of the response
-	MaxHeaderBytes int           // maximum size of request headers, DefaultMaxHeaderBytes if 0
-	TLSConfig      *tls.Config   // optional TLS config, used by ListenAndServeTLS
+	Addr         string        // TCP address to listen on, ":http" if empty
+	Handler      Handler       // handler to invoke, http.DefaultServeMux if nil
+	ReadTimeout  time.Duration // maximum duration before timing out read of the request
+	WriteTimeout time.Duration // maximum duration before timing out write of the response
+	TLSConfig    *tls.Config   // optional TLS config, used by ListenAndServeTLS
+
+	// MaxHeaderBytes controls the maximum number of bytes the
+	// server will read parsing the request header's keys and
+	// values, including the request line. It does not limit the
+	// size of the request body.
+	// If zero, DefaultMaxHeaderBytes is used.
+	MaxHeaderBytes int
 
 	// TLSNextProto optionally specifies a function to take over
 	// ownership of the provided TLS connection when an NPN