Penso che questa soluzione trovata su XDA faccia proprio al caso tuo :
Hi,
I'm running Marshmallow on my Nexus 5 and unfortunately svc data enable/disable stopped working for me. I always got a "killed" right away.
I found a workaround though. When calling su you have to provide a context:
su -cn u:r:system_app:s0
svc data disable/enable
This is working for me. Hope it's useful for some of you. The -cn switch is only available in SuperSU afaik.
You can read more on the topic here:https://su.chainfire.eu/#selinux-contexts-switching-why