reworks to clear shared_ptr<> of both command and data terminals
and having DTE own it. When we swith to CMUX mode the ownership is transfered to CMux terminal
* BG96 needs a small pause between CMUX command reception and actual use
of the CMUX mode
* Correct CMUX payload reception to check FT_UIH message type (P/F flag
could be cleared or set)
Closes https://github.com/espressif/esp-protocols/issues/33