mwifiex: define TDLS idle timeout macro with units

The unit of this timeout is in seconds.

Reported-by: Paul Stewart <pstew@chromium.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>