To be in line with other interfaces, when deleting the driver and it's glue layer to esp-netif, we DO NOT delete the related esp-netif (since is was allocated and created outside of the glue code and it works the same way in esp-eth and esp-wifi driver/glue layers).
Closes https://github.com/espressif/esp-idf/issues/5486
Addressing stability of pppos test:
* listing active network interfaces for presence of "ppp0" interface
* fixed IPv6 address regex to prevent ttfw accept partial address only
(less than 8 octets)
* workaround crash after exiting app_main()
Fu Hanxi