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
Ref #272
* Fix some lwip api bugs * Added PPP_SUPPORT parameter to lwip Kconfig * Added example pppos_client Merges #272 https://github.com/espressif/esp-idf/pull/272