wifi: mt76: update beacon size limitation

To accommodate 11v MBSSID IE and support maximum 16 MBSSIDs, expand the
beacon size limitation for beacon and inband discovery commands.

Co-developed-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Co-developed-by: Money Wang <money.wang@mediatek.com>
Signed-off-by: Money Wang <money.wang@mediatek.com>
Signed-off-by: MeiChia Chiu <meichia.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>