fix dhcp6 in upstream lwIP (#5560)

Author: d-a-v

libraries/ESP8266WiFi/examples/IPv6/IPv6.ino

@@ -54,8 +54,6 @@ void status(Print& out) {
   out.println(F("------------------------------"));
   out.println(ESP.getFullVersion());
 
-  dns_setserver(DNS_MAX_SERVERS - 1, IPAddress(8, 8, 8, 8));
-
   for (int i = 0; i < DNS_MAX_SERVERS; i++) {
     IPAddress dns = WiFi.dnsIP(i);
     if (dns.isSet()) {

tools/sdk/lib/liblwip6-1460-feat.a

@@ -1,5 +1,5 @@
 // generated by makefiles/make-lwip2-hash
 #ifndef LWIP_HASH_H
 #define LWIP_HASH_H
-#define LWIP_HASH_STR "STABLE-2_1_2_RELEASE/glue:1.0-5-g51b2d6c"
+#define LWIP_HASH_STR "STABLE-2_1_2_RELEASE/glue:1.0-6-g4670dfc"
 #endif // LWIP_HASH_H