As noticed by Jarek Poplawski <jarkao2@o2.pl>, the timer removal in
gen_kill_estimator races with the timer function rearming the timer.
Check whether the timer list is empty before rearming the timer
in the timer function to fix this.
Signed-off-by: Patrick McHardy <kaber@trash.net> Acked-by: Jarek Poplawski <jarkao2@o2.pl> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Adrian Bunk <bunk@stusta.de>