wifi: mt76: mt7996: fix invalid NSS setting when TX path differs from NSS

wifi: mt76: mt7996: fix invalid NSS setting when TX path differs from NSS

The maximum TX path and NSS may differ on a band. For example, one variant
of the MT7992 has 5 TX paths and 4 NSS on the 5 GHz band. To address this,
add orig_antenna_mask to record the maximum NSS and prevent setting an
invalid NSS in mt7996_set_antenna().

Fixes: 69d54ce7491d ("wifi: mt76: mt7996: switch to single multi-radio wiphy")
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://patch.msgid.link/20250515032952.1653494-5-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>