rtw88: fix non-increase management packet sequence number

In previous setting, management packets' sequence numbers will
not increase and always stay at 0. Add hw sequence number support
for mgmt packets.
The table below shows different sequence number setting in the
tx descriptor.

seq num ctrl      | EN_HWSEQ | DISQSELSEL | HW_SSN_SEL
------------------------------------------------------
sw ctrl           |    0     |    N/A     |    N/A
hw ctrl per MACID |    1     |     0      |    N/A
hw ctrl per HWREG |    1     |     1      |HWREG(0/1/2/3)

Signed-off-by: Tzu-En Huang <tehuang@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200326020408.25218-1-yhchuang@realtek.com