Allow port update() to modify security groups.

Author: kaecyra

lib/OpenCloud/Networking/Resource/Port.php

@@ -78,7 +78,8 @@ class Port extends PersistentResource
 
     protected $updateKeys = array(
         'name',
-        'deviceId'
+        'deviceId',
+        'securityGroups'
     );
 
     /**