esp32/ppp_set_auth: Add pppapi_set_auth from ESP-IDF.

This function was made private/static in IDF commit
c67f4c2b4c2bb4b7740f988fc0f8a3e911e56afe, so it add back here.

Signed-off-by: Damien George <damien@micropython.org>

ports/esp32/ppp_set_auth.h

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// The pppapi_set_auth function was made static in the ESP-IDF, so it's re-added here.
+// See ESP-IDF commit c67f4c2b4c2bb4b7740f988fc0f8a3e911e56afe
+
+#pragma once
+
+#include "esp_netif.h"
+
+#ifdef CONFIG_ESP_NETIF_TCPIP_LWIP
+
+#include "lwip/netif.h"
+
+typedef struct ppp_pcb_s ppp_pcb;
+
+void pppapi_set_auth(ppp_pcb *pcb, u8_t authtype, const char *user, const char *passwd);
+
+#endif