brcmfmac: screening firmware event packet

Firmware uses asynchronized events as a communication method to the
host. The event packets are marked as ETH_P_LINK_CTL protocol type. For
SDIO and PCIe bus, this kind of packets are delivered through virtual
event channel not data channel. This patch adds a screening logic to
make sure the event handler only processes the events coming from the
correct channel.

Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Signed-off-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>