extra_free_kbytes.sh is used by init to set /sys/vm/watermark_scale_factor
value. Allow init to execute extra_free_kbytes.sh and the script to access
/proc/sys/vm/watermark_scale_factor and /proc/sys/vm/extra_free_kbytes
files.
Bug: 109664768
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I55ec07e12a1cc5322cfdd4a48d0bdc607f45d832