Add source code for sdk_wifi_param_save_protect() and a compile time,
WIFI_PARAM_SAVE, option to skip writing the wifi state to flash. This
avoids wear on the flash and does not appear to be necessary when the
app initializes the state anyway.
Define WIFI_PARAM_SAVE to 0 for the wificfg example.
* When IPv6 is enabled the http server and the captive portal dns now also
accept IPv6 connections. The interface and peer IPv6 address are now also
reported.
* The http server no longer redirects <name>.local to an IP address for better
integration with mDNS.
* Add mDNS support, for the extras/mdnsresponder or the LWIP mDNS responder,
and enable the LWIP mDNS responder for examples/wificfg.
