mt76: mt7603: fix initialization of max rx length

The previous version only accidentally disabled A-MSDU deaggregation by
using the wrong mask for rx length configuration, which left previous
length value in place.
Fix the length and initialize the register completely to keep A-MSDU
de-aggregation remaining disabled

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