HTT_H2T_MSG_TYPE_MGMT_TX msg in 10.4 firmware carries additional
4 byte in htt_mgmt_tx_desc where it tells to firmware that at what
rate mgmt frame has to go out in the air. It's an optional parameter,
setting this field to zero will force firmware to choose auto rate
and send the frame out.

Those 4 byte info is missed out in the current code and 10.4 firmware
ended up reading some junk in those 4 byte and sometime malfunctioning.

Fix it by adding 4 byte in struct htt_mgmt_tx_desc. Non 10.4 firmware
will not process those four byte. So, adding 4 byte at the end of
struct htt_mgmt_tx_desc will not create any impact on other chipset.

Signed-off-by: Raja Mani <rmani@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>