[Bug] [netdev] ping still applies delay after the last packet and calls rt_thread_delay(0) returning -RT_EINVAL #11865

In netdev_cmd_ping(), the loop tries to skip the inter-packet delay on the final ping:

/* if the response time is more than NETDEV_PING_DELAY, no need to delay */
delay_tick = ((rt_tick_get() - start_tick) > NETDEV_PING_DELAY) || (index == times) ? 0 : NETDEV_PING_DELAY;
rt_thread_delay(delay_tick);

Two issues:

1. The index == times condition is never true inside the loop (index < times), so the delay is still applied after the last packet, contrary to the comment.
2. When delay_tick becomes 0, rt_thread_delay(0) is still called and returns -RT_EINVAL (invalid argument).

Proposed fix: compute the actual elapsed time, skip the delay on the last packet via index != times - 1, and only call rt_thread_delay() when delay_tick > 0.