ath9k: Set RX filter based to allow broadcast Action frame RX

Advertise support for multicast frame registration and update the RX
filter based on the recently added FIF_MCAST_ACTION to allow broadcast
Action frames to be received. This is needed for Device Provisioning
Protocol (DPP) use cases that use broadcast Public Action frames.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200426084733.7889-1-jouni@codeaurora.org