Fix rx_buffer type in TCP example (IDFGH-10780)

[Daniel-Chin]

In the example projects for protocol/socket/TCP..., the rx_buffer was of type char*. I changed it to uint8_t*.

Semantically, TCP transmits a byte stream, not a char stream. Using char* in the example can potentially confuse beginners.

Let me know if there are further considerations.

[CLAassistant]

All committers have signed the CLA.

[espressif-abhikroy]

I concur with your assessment regarding a standard TCP connection. However, in the context of this specific example, the payload has been hardcoded as an ASCII string. Therefore, the present implementation is accurate and does not require any alterations.

[Daniel-Chin]

I concur with your assessment regarding a standard TCP connection. However, in the context of this specific example, the payload has been hardcoded as an ASCII string. Therefore, the present implementation is accurate and does not require any alterations.

Understood.