Remove KEEP_ALIVE_HACK to avoid waking up the device periodly.
The workaround it's added by:
commit 6546fa39c7
Author: Gregory Nutt <gnutt@nuttx.org>
Date: Tue Aug 12 11:12:00 2014 -0600
Tickless Stuff: Back out the risky timer operations when the ready-to-run
list is modified. That is unsafe. An ugly workaround is just to keep an
interval timer going all of the time with a minimum duration equal to the
timeslice interval.
But look like it doesn't needed anymore.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
50e2269642