mac80211: Increase timeouts for station polling

Do a probe request every 30 seconds, and wait for probe response,
half a second This should lower the traffic that card sends, thus save
power Wainting longer for response makes probe more robust against
'slow' access points

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>