mac80211: do not overwrite the sequence number if requested

Check if the Tx control flag is set to prevent sequence number overwrites,
and if so, do not assign a new sequence number to the transmitted frame.

Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@kuleuven.be>
Link: https://lore.kernel.org/r/20200723100153.31631-3-Mathy.Vanhoef@kuleuven.be


Signed-off-by: Johannes Berg <johannes.berg@intel.com>