cpu/esp8266: lwIP dummy functions added

Defines a number of lwIP functions that are required as symbols by Espressif's SDK libraries. These functions are only dummies without real functionality. Using these functions instead of real lwIP functions provided with the SDK saves arround 4 kBytes of RAM.

cpu/esp8266/sdk/lwip.c

+/*
+ * Copyright (C) 2018 Gunar Schorcht
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_esp8266
+ * @{
+ *
+ * @file
+ * @brief       lwIP functions required as symbols by the SDK
+ *
+ * This file defines a number of lwIP functions that are required as symbols by
+ * Espressif's SDK libraries. Since RIOT doesn't need lwIP, these functions are
+ * only dummies without real functionality. Using these functions instead of
+ * the lwIP functions as provided with the SDK saves arround 4 kBytes of RAM.
+ *
+ * @author      Gunar Schorcht <gunar@schorcht.net>
+ * @}
+ */
+
+#include "lwip/err.h"
+#include "lwip/ip_addr.h"
+#include "lwip/netif.h"
+#include "lwip/pbuf.h"
+#include "lwip/tcp_impl.h"
+#include "netif/etharp.h"
+
+#define ENABLE_DEBUG    (0)
+#include "debug.h"
+#include "log.h"
+
+#ifndef ERR_OK
+#define ERR_OK 0
+#endif
+
+const struct eth_addr ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}};
+
+err_t ethernet_input(struct pbuf *pb, struct netif* netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)pb;
+    (void)netif;
+    return ERR_OK;
+}
+
+err_t etharp_output(struct netif *netif, struct pbuf *q, ip_addr_t *ipaddr)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    (void)q;
+    (void)ipaddr;
+    return ERR_OK;
+}
+
+err_t etharp_request(struct netif *netif, ip_addr_t *ipaddr)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    (void)ipaddr;
+    return ERR_OK;
+}
+
+void etharp_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void etharp_cleanup_netif(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+}
+
+void dhcp_cleanup(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+}
+
+err_t dhcp_start(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    return ERR_OK;
+}
+
+err_t dhcp_renew(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    return ERR_OK;
+}
+
+err_t dhcp_release(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    return ERR_OK;
+}
+
+void dhcp_stop(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+}
+
+void dhcp_network_changed(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+}
+
+void dhcp_coarse_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void dhcp_fine_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void dhcps_start(struct ip_info *info)
+{
+    DEBUG("%s\n", __func__);
+    (void)info;
+}
+
+void dhcps_stop(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void dhcps_coarse_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+union tcp_listen_pcbs_t tcp_listen_pcbs;
+struct tcp_pcb *tcp_active_pcbs;
+struct tcp_pcb *tcp_tw_pcbs;
+
+void tcp_seg_free(struct tcp_seg *seg)
+{
+    DEBUG("%s\n", __func__);
+    (void)seg;
+}
+
+void tcp_abort (struct tcp_pcb *pcb)
+{
+    DEBUG("%s\n", __func__);
+    (void)pcb;
+}
+
+void tcp_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void igmp_init(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+err_t igmp_start(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    return ERR_OK;
+}
+
+err_t igmp_stop(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+    return ERR_OK;
+}
+
+void igmp_report_groups(struct netif *netif)
+{
+    DEBUG("%s\n", __func__);
+    (void)netif;
+}
+
+void igmp_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void dns_init(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+void dns_tmr(void)
+{
+    DEBUG("%s\n", __func__);
+}
+
+uint32_t espconn_init(uint32 arg)
+{
+    DEBUG("%s\n", __func__);
+    (void)arg;
+    return 1;
+}