brcmfmac: ignore IF event if firmware indicates it

Not every IF event from the firmware needs to result in a
related interface, netdev or wdev, on the host. This is
indicated in the event message. Handle that flag and effectively
ignore the firmware event.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>