This patch configures the beacon timers with beacon interval
and beacon period passed through vif.bss_conf. Also cache the
currecnt beacon configuration which will be used to configure
the beacon timers when the driver triggers it after reset.
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>