For PMF case, the action,deauth,disassoc management need to encrypt
by hardware, it need to reserve 8 bytes for encryption, otherwise
the packet will be sent out with error format, then PMF case will
fail.

After add the 8 bytes, it will pass the PMF case.

Tested with QCA6174 SDIO with firmware
WLAN.RMH.4.4.1-00005-QCARMSWP-1.
Signed-off-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>