wifi: mt76: mt7915: also MT7981 is 3T3R but nss2 on 5 GHz band

Just like MT7916 also MT7981 can handle 3T3R DBDC frontend and should
hence be included in the corresponding conditional expression in the
driver. Add it.

Fixes: 6bad146d ("wifi: mt76: mt7915: add support for MT7981")
Signed-off-by: StanleyYP Wang <StanleyYP.Wang@mediatek.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/main.c

@@ -1059,8 +1059,9 @@ mt7915_set_antenna(struct ieee80211_hw *hw, u32 tx_ant, u32 rx_ant)
 
 	phy->mt76->antenna_mask = tx_ant;
 
-	/* handle a variant of mt7916 which has 3T3R but nss2 on 5 GHz band */
-	if (is_mt7916(&dev->mt76) && band && hweight8(tx_ant) == max_nss)
+	/* handle a variant of mt7916/mt7981 which has 3T3R but nss2 on 5 GHz band */
+	if ((is_mt7916(&dev->mt76) || is_mt7981(&dev->mt76)) &&
+	    band && hweight8(tx_ant) == max_nss)
 		phy->mt76->chainmask = (dev->chainmask >> chainshift) << chainshift;
 	else
 		phy->mt76->chainmask = tx_ant << (chainshift * band);