SuperSU 2.50 allows ROOT in selinux enforcing mode, so the permissive hack is not needed anymore. You need to flash one of these modified stock boot.imgs for your device: http://forum.xda-developers.com/apps/supersu/wip-android-6-0-marshmellow-t3219344
-Flash boot.img via fastboot / TWRP (unzip it and push the boot.img to your device, chose image to install - boot partition)
-Boot into recovery
-flash latest hC: N5 and N6
This boot.img also disables security warning on bootup!