esp8266/modmachine: In lightsleep, only waiti if wifi is turned off.

Otherwise the STA interface can't do DTIM sleeping correctly and power
consumption goes up.

ports/esp8266/modmachine.c

@@ -105,10 +105,14 @@ STATIC mp_obj_t machine_lightsleep(size_t n_args, const mp_obj_t *args) {
         }
         max_us = max_ms * 1000;
     }
+    uint32_t wifi_mode = wifi_get_opmode();
     uint32_t start = system_get_time();
     while (system_get_time() - start <= max_us) {
         ets_event_poll();
-        asm("waiti 0");
+        if (wifi_mode == NULL_MODE) {
+            // Can only idle if the wifi is off
+            asm("waiti 0");
+        }
     }
     return mp_const_none;
 }