esp32: fix WiFi stop bug in WiFi/BT coexist mode
esp32: fix WiFi stop bug in WiFi/BT coexist mode

This fix includes following changes:
1. Fix the bug that esp_restart()/esp_wifi_stop() sometimes fails in WiFi/BT coexist mode.
2. Add a timer for WiFi stop and stop WiFi forcibly once the timer expires.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf