rsi: add interface changes for ap mode

AP mode is handled in add_interface callback of mac80211.
Also for AP mode, sending rx filter frame to disallow beacons
to host is added. Station structures are initialized to NULL.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>