cfg80211: increse bss expire time

The background scan completion takes more time when the station is
having heavy uplink traffic. The scan state machine decides to fall
back to home channel on every off-channel visit when there are pending
frames in tx queue. bgscan completion took ~30sec on dual band US
regulatory card.

scan period = (20 active channels * probe timeout) +
              (12 passive channels * passive probe timeout) +
              (32 * timeout on home channel) +
              (32 * flush timeout)

Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>