[PATCH] softmac: reduce scan dwell time

It currently takes something like 8 seconds to do a scan, because we
spend half a second on each channel. Reduce that time to 20ms per
channel.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>