openocd: add keep_alive during command sleep

The command sleep holds the host CPU until it completes.
Send keep_alive to GDB, so it will not timeout.

Change-Id: I92e9c5fc871b4e6a7695cdc449ca9fb3c1f1d9ec
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6770
Tested-by: jenkins
Reviewed-by: Jan Matyas <matyas@codasip.com>

src/helper/command.c

@@ -1145,6 +1145,7 @@ COMMAND_HANDLER(handle_sleep_command)
 		int64_t then = timeval_ms();
 		while (timeval_ms() - then < (int64_t)duration) {
 			target_call_timer_callbacks_now();
+			keep_alive();
 			usleep(1000);
 		}
 	} else