mac80211_hwsim: Claim support for setting Beacon frame TX legacy rate

mac80211 takes care of rate control for the Beacon frames, so all
mac80211_hwsim needs to do here is advertise support for this.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Link: https://lore.kernel.org/r/20200425155713.25687-5-jouni@codeaurora.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>