`softAPIPv6` and `localIPv6` renamed in Espressif SDK 3.0

[hn3000]

As originally posted in #135

The methods softAPIPv6() and localIPv6() were renamed as part of Espressif's "3.0.0 Network Refactoring (#8760)" with the comment "* Rename IPv6 getters to clarify that they are returning LinkLocal address";
the corresponding diffs are:

-    IPAddress softAPIPv6();
+    IPAddress softAPlinkLocalIPv6();

and:

-    IPAddress localIPv6();
+    IPAddress linkLocalIPv6();