Fix metrics path not using command-line argument value (prometheus#904)

Signed-off-by: Hugo Hromic <[email protected]>
Signed-off-by: Stephan Windischmann <[email protected]>

main.go

@@ -220,7 +220,7 @@ func main() {
 		}
 	}()
 
-	http.Handle("/metrics", promhttp.Handler()) // Normal metrics endpoint for SNMP exporter itself.
+	http.Handle(*metricsPath, promhttp.Handler()) // Normal metrics endpoint for SNMP exporter itself.
 	// Endpoint to do SNMP scrapes.
 	http.HandleFunc(proberPath, func(w http.ResponseWriter, r *http.Request) {
 		handler(w, r, logger)