brcmfmac: fix skb priority handling

SKBs can come with a prioriy. Currently a priority of 0..7 is
assumed. But this assumption is incorrect. To fix this any
priority of 0 or higher then 7 will be adjusted by calling
cfg80211_classify8021d

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