cfg80211: lower dynamic PS timeout to 100ms

The default of 500ms is pretty high, and leads
to the device being awake at least 50% of the
time under such light traffic conditions as a
simple 1 second interval ping. Reduce to just
100ms -- it should have a similar effect while
providing a better sleep time.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>