fix: erroneous high value for gateway received bytes metrics (#8978)

http.Request.ContentLength can be negative, which affects
the gateway_s3_bytes_received value in Prometheus output.

The commit only increases the value of the total received bytes
in gateway mode when r.ContentLength is greater than zero.

cmd/gateway-common.go

@@ -434,7 +434,9 @@ func (m MetricsTransport) RoundTrip(r *http.Request) (*http.Response, error) {
 	metered := shouldMeterRequest(r)
 	if metered && (r.Method == http.MethodGet || r.Method == http.MethodHead) {
 		m.Metrics.IncRequests(r.Method)
-		m.Metrics.IncBytesSent(r.ContentLength)
+		if r.ContentLength > 0 {
+			m.Metrics.IncBytesSent(uint64(r.ContentLength))
+		}
 	}
 	// Make the request to the server.
 	resp, err := m.Transport.RoundTrip(r)
@@ -442,7 +444,9 @@ func (m MetricsTransport) RoundTrip(r *http.Request) (*http.Response, error) {
 		return nil, err
 	}
 	if metered && (r.Method == http.MethodGet || r.Method == http.MethodHead) {
-		m.Metrics.IncBytesReceived(resp.ContentLength)
+		if r.ContentLength > 0 {
+			m.Metrics.IncBytesReceived(uint64(resp.ContentLength))
+		}
 	}
 	return resp, nil
 }