espnet: WIP support for on-chip WiFi on an ESP32C3

Work in progress. Does not work yet.

Some notes:

  - This requires some changes to TinyGo, look at the espnet branch.
  - The  next step is probably defining all the functions in
    g_wifi_osi_funcs (see espnet.c). Right now it hangs in
    esp_wifi_init_internal, probably a NULL pointer dereference.
  - This is only for the ESP32-C3. This will require some work to work
    on other chips from Espressif.

espnet/ap.go

@@ -0,0 +1,40 @@
+package espnet
+
+/*
+#cgo CFLAGS: -DCONFIG_IDF_TARGET_ESP32C3
+#cgo CFLAGS: -Iinclude
+#cgo CFLAGS: -Iesp-idf/components/esp_common/include
+#cgo CFLAGS: -Iesp-idf/components/esp_event/include
+#cgo CFLAGS: -Iesp-idf/components/esp_netif/include
+#cgo CFLAGS: -Iesp-idf/components/esp_wifi/include
+
+#cgo LDFLAGS: -Lesp-idf/components/esp_wifi/lib/esp32c3 -lnet80211 -lpp -lphy -lmesh -lcore
+#cgo LDFLAGS: -Tesp-idf/components/esp_rom/esp32c3/ld/esp32c3.rom.ld
+
+#include "esp_private/wifi.h"
+#include "esp_wifi_types.h"
+#include "espnet.h"
+*/
+import "C"
+
+type ESPWiFi struct {
+}
+
+var WiFi = &ESPWiFi{}
+
+type Config struct {
+}
+
+var internalConfig = C.wifi_init_config_t{
+	osi_funcs: &C.g_wifi_osi_funcs,
+}
+
+func (wifi ESPWiFi) Configure(config Config) error {
+	return makeError(C.esp_wifi_init_internal(&internalConfig))
+}
+
+func (wifi ESPWiFi) AccessPointMAC() ([6]byte, error) {
+	var mac [6]byte
+	errCode := C.esp_wifi_get_mac(C.ESP_IF_WIFI_AP, &mac[0])
+	return mac, makeError(errCode)
+}