mt76: mt7921: drop offload_flags overwritten

offload_flags have to be dropped for mt7921 because mt76.omac_idx 0 would
always run as station mode that would cause Tx encapsulation setting
is not applied to mac80211.

Also, drop IEEE80211_OFFLOAD_ENCAP_4ADDR too because it is not really
being supported.

Fixes: e0f9fdda ("mt76: mt7921: add ieee80211_ops")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/main.c

@@ -318,12 +318,6 @@ static int mt7921_add_interface(struct ieee80211_hw *hw,
 		mtxq->wcid = &mvif->sta.wcid;
 	}
 
-	if (vif->type != NL80211_IFTYPE_AP &&
-	    (!mvif->mt76.omac_idx || mvif->mt76.omac_idx > 3))
-		vif->offload_flags = 0;
-
-	vif->offload_flags |= IEEE80211_OFFLOAD_ENCAP_4ADDR;
-
 out:
 	mt7921_mutex_release(dev);