do_syscall: Call schedule() when runq_len > 1

This optimization make the offloading thread quickly yield to
another thread. Without this, it yileded only after the interval timer
set the rescheduling flag.

Change-Id: Ida3b17ed94782d5d1af0185a96b1f50d9db8d244

kernel/syscall.c

@@ -332,6 +332,7 @@ long do_syscall(struct syscall_request *req, int cpu, int pid)
 			v = get_this_cpu_local_var();
 
 			if (v->flags & CPU_FLAG_NEED_RESCHED ||
+			    v->runq_len > 1 ||
 			    req->number == __NR_sched_setaffinity) {
 				do_schedule = 1;
 			}