server/telnet: Always allow 'exit' command

The telnet 'exit' command is only available in the execution phase of
OpenOCD. Thus, a telnet session cannot be closed via 'exit' if OpenOCD
is started with 'noinit'. Make the 'exit' command always available.

Change-Id: I14447ecde63e579f1c523d606f048ad29cc84a35
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8379
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins

src/server/telnet_server.c

@@ -982,7 +982,7 @@ static const struct command_registration telnet_command_handlers[] = {
 	{
 		.name = "exit",
 		.handler = handle_exit_command,
-		.mode = COMMAND_EXEC,
+		.mode = COMMAND_ANY,
 		.usage = "",
 		.help = "exit telnet session",
 	},