map loglevel (int-value) to log-message, as well

src/Monolog/Formatter/LogstashFormatter.php

@@ -83,6 +83,9 @@ class LogstashFormatter extends NormalizerFormatter
         if (isset($record['level_name'])) {
             $message['level'] = $record['level_name'];
         }
+        if (isset($record['level'])) {
+            $message['level_num'] = $record['level'];
+        }
         if ($this->applicationName) {
             $message['type'] = $this->applicationName;
         }

tests/Monolog/Formatter/LogstashFormatterTest.php

@@ -45,6 +45,7 @@ class LogstashFormatterTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals('log', $message['message']);
         $this->assertEquals('meh', $message['channel']);
         $this->assertEquals('ERROR', $message['level']);
+        $this->assertEquals(Logger::ERROR, $message['level_num']);
         $this->assertEquals('test', $message['type']);
         $this->assertEquals('hostname', $message['host']);