gp->reset_task_pending is always set right before reset_task is
scheduled and as there is no synchronization between the setting and
scheduling, busy looping on reset_task_pending before flushing
reset_task doesn't really buy anything.

Directly flush gp->reset_task on suspend and cancel on detach.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org