ath10k: parse Rx MAC timestamp in mgmt frame for FW 10.4

Check and parse Rx MAC timestamp when firmware sets its flag
to status variable.
10.4 firmware adds it in Rx beacon frame only at this moment.
Drivers and mac80211 may utilize it to detect such clockdrift
or beacon collision and use the result for beacon collision
avoidance.

Signed-off-by: Peter Oh <poh@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>