picow: Implement stop_station

Weirdly we have to stop the AP too (which we never started),
or cyw43_tcpip_link_status still reports that STA is connected.
As long as AP mode isn't implemented, this doesn't matter and
we can just do it.

Author: jepler

ports/raspberrypi/common-hal/wifi/Radio.c

@@ -158,6 +158,13 @@ void common_hal_wifi_radio_start_station(wifi_radio_obj_t *self) {
 }
 
 void common_hal_wifi_radio_stop_station(wifi_radio_obj_t *self) {
+    cyw43_wifi_leave(&cyw43_state, CYW43_ITF_STA);
+    // This is wrong, but without this call the state of ITF_STA is still
+    // reported as CYW43_LINK_JOIN (by wifi_link_status) and CYW43_LINK_UP
+    // (by tcpip_link_status). Until AP support is added, we can ignore the
+    // problem.
+    cyw43_wifi_leave(&cyw43_state, CYW43_ITF_AP);
+    bindings_cyw43_wifi_enforce_pm();
 }
 
 void common_hal_wifi_radio_start_ap(wifi_radio_obj_t *self, uint8_t *ssid, size_t ssid_len, uint8_t *password, size_t password_len, uint8_t channel, uint8_t authmode, uint8_t max_connections) {