mt76: mt76x02: fix tx reordering on rate control probing without a-mpdu

To avoid aggregating rate control probing packets with other traffic, and to
ensure that the probing rate gets used, probing packets get assigned a different
internal queueing priority.
This causes packets to be transmitted in a different order, which is compensated
by the receiver side reordering.
However, if A-MPDU is disabled, this reordering can become visible to upper
layers on the receiver side. Disable the priority change if A-MPDU is disabled.

Signed-off-by: Felix Fietkau <nbd@nbd.name>