fix switching to static address with lwip2

For some reason, ip address is not propagated in a visible way for lwip2
when switching to static address (wifi.config()) *after* wifi.begin().

This patch calls lwip-v1.4's netif_set_addr() with the new ip address to set
all things up, just like it is done and right when wifi.begin() is called
after wifi.config().

Also tested when IPv6 is enabled.

fixes esp8266#5839
fixes esp8266#6024

Author: d-a-v

libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp

@@ -247,6 +247,13 @@ wl_status_t ESP8266WiFiSTAClass::begin() {
  * @param dns1       Static DNS server 1
  * @param dns2       Static DNS server 2
  */
+
+#if LWIP_VERSION_MAJOR != 1
+#undef netif_set_addr // need to call lwip-v1.4 netif_set_addr()
+extern "C" struct netif* eagle_lwip_getif (int netif_index);
+extern "C" void netif_set_addr (struct netif* netif, ip4_addr_t* ip, ip4_addr_t* netmask, ip4_addr_t* gw);
+#endif
+
 bool ESP8266WiFiSTAClass::config(IPAddress local_ip, IPAddress arg1, IPAddress arg2, IPAddress arg3, IPAddress dns2) {
 
   if(!WiFi.enableSTA(true)) {
@@ -310,6 +317,11 @@ bool ESP8266WiFiSTAClass::config(IPAddress local_ip, IPAddress arg1, IPAddress a
       dns_setserver(1, dns2);
   }
 
+#if LWIP_VERSION_MAJOR != 1
+  // trigger address change by calling lwip-v1.4 api
+  netif_set_addr(eagle_lwip_getif(STATION_IF), &info.ip, &info.netmask, &info.gw);
+#endif
+
   return true;
 }