MINOR: task: limit the remote thread wakeup to the global runqueue only

MINOR: task: limit the remote thread wakeup to the global runqueue only

The test in __task_wakeup() to figure if the remote threads are sleeping
doesn't make sense outside of the global runqueue test, since there are
only two possibilities here: local runqueue or global runqueue, hence a
sleeping thread is another one and can only happen when sending to the
global run queue. Let's move the test inside the "if" block.