* netif.stop() moved after setting the transition callback
* send PPP escape sequence if enabled before waiting for transition to
complete
* add newline character before sync() command (after the "+++")
Closes https://github.com/espressif/esp-protocols/issues/692
* bool flag to defragment CMUX payload (useful for devices that send longer messages)
* int flag to force a delay between creating virtual terminals (useful for chatty devices that send some requests)