mt76: mt7663: fix when beacon filter is being applied

HW beacon filter command is being applied until we're in associated state
because the command would rely on the associated access point's beacon
interval and DTIM information.

Fixes: 7124198a ("mt76: mt7615: enable beacon filtering by default for offload fw")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>