Based on his revision 2d290a24a0914be88e5ca4ac7b1018392fe75fe2
(https://github.com/djphoenix/nodemcu-firmware).
All LWIP callback handling changed to use the NodeMCU task interface
to make it usable on RTOS.
IPv4 assumptions have been removed, and this net module /should/ now
be IPv6 ready, but aside from compilation no testing has been done
in this area.
SSL integration points not touched - some work needed there once we
have an mbedTLS module.
be5dafb264