The ESP32 PPP implementation predates the generic
implementation in extmod. The new extmod
implementation has a few advantages such as a
better deinitialisation procedure (the ESP32
implemementation would not clean up properly and
cause crashes if recreated) and using the UART IRQ
functionality instead of running a task to read
data from the UART.
This change restructures the ESP implementation to
be much closer to the new extmod version, while
also bringing a few tiny improvements from the
ESP32 version to the extmod version. The diff
between extmod/network_ppp_lwip.c and
ports/esp32/network_ppp.c is now a small set of
easy to review ESP32 port-specific changes.
Signed-off-by: Daniël van de Giessen <daniel@dvdgiessen.nl>