wifi: mt76: mt7996: fix null pointer deref in mt7996_conf_tx()

wifi: mt76: mt7996: fix null pointer deref in mt7996_conf_tx()

If a link does not have an assigned channel yet, mt7996_vif_link returns
NULL. We still need to store the updated queue settings in that case, and
apply them later.
Move the location of the queue params to within struct mt7996_vif_link.

Fixes: c0df2f0caa8d ("wifi: mt76: mt7996: prepare mt7996_mcu_set_tx for MLO support")
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250929111723.52486-1-nbd@nbd.name
Signed-off-by: Felix Fietkau <nbd@nbd.name>