soc: xtensa: partial fix of socket misuse and refine the code

1. Improve the firmware transfer reliability by fixing the misuse
of the socket. Fix the most frequent occurence of the common `recv()`
bug described here:

https://docs.python.org/3/howto/sockets.html#using-a-socket



The longer term fix is to switch to a higher level API like Python
Remote Objects.

2. Not rely on the client's command to disconnect. Previously we
rely on the SIGINT to send stop_command to the server, but it does
not work well in some environments. Refine the whole logic and the
sever disconnect service by checking if the client is alive or not.

These changes make the client-server-based cavstool more stable.

Fixes #46864

Signed-off-by: Enjia Mai <enjia.mai@intel.com>