wifi: mt76: fix queue assignment for deauth packets

When running in AP mode and deauthenticating a client that's in powersave
mode, the disassoc/deauth packet can get stuck in a tx queue along with
other buffered frames. This can fill up hardware queues with frames
that are only released after the WTBL slot is reused for another client.

Fix this by moving deauth packets to the ALTX queue.

Reported-by: Chad Monroe <chad.monroe@adtran.com>
Link: https://patch.msgid.link/20250707154702.1726-2-nbd@nbd.name


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