calling esp_netif_up() and esp_netif_down() was not supported if the
underlying netif wos of ppp type. Updated the code to enable setting
these interfaces up/down and registered actions in moden_netif glue for
connection/disconnection events to set the netif up/down.
When library users call esp_stop_ppp(), it is expected that the PPP link
is closed and the DCE is moved into command mode.
If the STOP event is not posted into the event loop, then the PPP stack
would not be turned off, resulting in the impossibility to switch into
command mode, as the modem is still sending PPP binary data.
Signed-off-by: Francesco Giancane <francesco.giancane@accenture.com>
Merges https://github.com/espressif/esp-idf/pull/4642
1. add support for ESP32 DTE
2. add support for SIM800/BG96 DCE
3. add PPPoS setup procedure
4. add support for SMS
5. add mqtt example after PPP connection established
