mac80211: copy configured beacon tx rate to driver

The user is allowed to change beacon tx rate (HT/VHT/HE) from hostapd.
This information needs to be passed to the driver when the rate control
is offloaded to the firmware. The driver capability of allowing beacon
rate is already validated in cfg80211, so simply passing the rate
information to the driver is enough.

Signed-off-by: Rajkumar Manoharan <rmanohar@codeaurora.org>
Link: https://lore.kernel.org/r/1601762658-15627-1-git-send-email-rmanohar@codeaurora.org
[adjust commit message slightly]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>