wifi: mt76: mt7603: fix tx queue of loopback packets

Use the correct WMM AC queue instead of the MGMT one to fix potential issues
with aggregation sequence number tracking. Drop non-bufferable packets.

Fixes: fca9615f ("mt76: mt7603: fix up hardware queue index for PS filtered packets")
Signed-off-by: Felix Fietkau <nbd@nbd.name>