* wificfg: remove the AP WEP mode option
The WEP mode does not appear to be implement in the sdk for the AP mode, and
defaults to open when WEP is requested which is probably not intended. Remove
the WEP option from the wifi config interface.
* lwip: enable mdns dns queries.
* wificfg: support mDNS on the softAP interface.
* 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.
* Correct checking of the AP password and SSID lengths.
* Only enable AP mode if it is really configured enabled.
* Only start the http server if wifi is enabled.
This patch gets the newlib standard stream descriptors playing well with the
lwip socket descriptors and the spiffs file descriptors. The LWIP_SOCKET_OFFSET
is now defined to be 3, rather than zero, to avoid clashing with the standard
stream descriptors, and the SPIFFS_FILEHDL_OFFSET is bumped up to start after
the lwip descriptors.
