fix(esp_netif): Fix missing IPv6 autoconfig for PPP netifs

Closes #13713

components/esp_netif/lwip/esp_netif_lwip_ppp.c

@@ -161,7 +161,7 @@ static void on_ppp_notify_phase(ppp_pcb *pcb, u8_t phase, void *ctx)
 #endif // PPP_NOTIFY_PHASE
 
 /**
- * @brief PPP low level output callback used to transmit data using standard esp-netif interafce
+ * @brief PPP low level output callback used to transmit data using standard esp-netif interface
  *
  * @param pcb PPP control block
  * @param data Buffer to write to serial port
@@ -247,6 +247,10 @@ esp_err_t esp_netif_start_ppp(esp_netif_t *esp_netif)
     }
 #endif
 
+#if ESP_IPV6_AUTOCONFIG
+    ppp_ctx->ppp->netif->ip6_autoconfig_enabled = 1;
+#endif
+
     ESP_LOGD(TAG, "%s: Starting PPP connection: %p", __func__, ppp_ctx->ppp);
     err_t err = ppp_connect(ppp_ctx->ppp, 0);
     if (err != ESP_OK) {