TCP socket: add the ability to manage Keep Alive mechanism on Linux

Some equipment need to be able to configure the Keep Alive mechanism to be able to monitor the activity off the other end of the connexion.

See https://datatracker.ietf.org/doc/html/rfc1122#page-101 about the RFC on the topic (although IT technology has evolved since this RFC has been issued).

Support of this functionnality is:

• fully available on Linux (see https://www.man7.org/linux/man-pages/man7/tcp.7.html)
• fully available on Windows (see https://learn.microsoft.com/en-us/windows/win32/winsock/so-keepalive and https://learn.microsoft.com/en-us/windows/win32/winsock/sio-keepalive-vals)
• not available on FreeRTOS or Zephyr

As the need expressed by customer is focused on Linux, one first step would be to add this functionnality on Linux for a start.