Reusable component in modem_tcp_client example implements a simple
mbedtls wrapper. This update add support for mbedtls deinit() and for
saving and restoring TLS session.
Similar to pppos-client, but without PPP mode.
This uses standard mqtt client and a loopback service that forwards the
TCP traffic from localhost to the modem and vice-versa.
(next step is to create a dedicated tcp-transport layer for modem)
Console example uses DCE commandable to demontrate how to handle URC
