android: lowmemorykiller: notify_trigger_active compatibility

Rename the "/sys/kernel/mm/lowmem_notify/notify_trigger_active" sysfs node
to "/sys/kernel/mm/lowmemorykiller/notify_trigger_active" to present the same
interface used by older kernels.

Change-Id: I49533fa005c965f5a4d6bd2f771e0f7ddfb1a8f3
Signed-off-by: Michael Vines <mvines@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>