qtnfmac: add interface ID to each packet

Add interface ID information to the tail of each transmitted packet
so that firmware can know to which interface the packet belongs to.
This is only needed if device supports HW switch capability.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>