As reported https://esp32.com/viewtopic.php?f=14&t=6171
event_callback() in sockets.c calls conn->socket-- to register
activity on a netconn which may not have any socket yet,
so any socket value < 0 indicates "no controlling socket"
for the netconn.
1. Put some lwip udp rx/tx relating functions to IRAM
2. Put some wifi rx/tx relating functions to IRAMa
3. Reduce wifi dynamic malloc from 4 to 1 for each ebuf
4. Update iperf example accordingly
5. Update libphy.a to v383
If the DNS request is dispatched and performed very quickly,
then it can complete before tcpip_callback() actually returns,
in which case we'll destroy the actual err_t error value passed
in the message. Use a local variable for the tcpip_callback
error code so that can't happen.
Resolves#269https://github.com/espressif/esp-idf/pull/269
1. Update wifi lib which contains ampdu and other optimizations
2. Add throughput code debug code
3. Other misc modification about throughput optimization
