* The mdns responder has been reworked to lower stack and memory usage. This is
a variation on the upstream code, it use malloc whereas the upstream code uses
pools. The high stack usage of the mdns responder was problem for
esp-open-rtos, so we might have to maintain the differences for now.
* Improved lwip core locking, and lock checking. Upstream improvements, that
need some added support from esp-open-rtos specific code. More core lock is
performed when calling from the esp-open-rtos code now, so a little safer. The
checking is not enforced, but projects might see warning messages and might
want to look into them.
* The esp-open-rtos lwip support has been sync'ed with the new freertos port
included with lwip. There are still some minor differences.
* A few lwip timer bugs have been resolved. This might help resolve some issues.
* Plus it picks up all the other upstream fixes and improvements.
* The default lwip stack has been lowered from 768 words to 480 words,
due to the reduced stack usage by the mdns responder.
Multicast frames were being dropped by ieee80211_output_pbuf. It appears to look
up the destination address using cnx_node_search which only has an entry for the
broadcast address (all ones). This patch modifies cnx_node_search to return the
broadcast cnx_node for the multicast addresses too.
This is needed to support services such as mDNS on the softap interface.
Also adds source code for sdk_cnx_rc_search, adding a null pointer dereference
check (that is not expected to be seen), and source code for sdk_cnx_remove_rc.
Also code for sdk_cnx_sta_leave, although disabled due to accessing static date, but it shows a reference to the netif->flags and the NETIF_FLAG_DHCP flag removed in lwip v2.
