The mgmt_rx event structure has been expanded.
Since the structure header is expanded the payload
(i.e. mgmt frame) is shifted by a few bytes. This
needs to be taken into account in order to support
both old and new firmware.

This introduces a fw_features to keep track of any
FW-related ABI/behaviour changes.
Signed-off-by: NMichal Kazior <michal.kazior@tieto.com>
Signed-off-by: NKalle Valo <kvalo@qca.qualcomm.com>