Modify usleep to rte_delay_us_sleep.

The minimum timeout unit of epoll_wati in interrupt mode is 1ms, which is not applicable to F-Stack and is abandoned directly.

Author: jfb8856606

lib/ff_dpdk_if.c

@@ -2181,7 +2181,7 @@ main_loop(void *arg)
 
         idle_sleep_tsc = rte_rdtsc();
         if (likely(idle && idle_sleep)) {
-            usleep(idle_sleep);
+            rte_delay_us_sleep(idle_sleep);
             end_tsc = rte_rdtsc();
         } else {
             end_tsc = idle_sleep_tsc;