wifi: mt76: mt792x: skip MLD header rewrite for 802.3 encap TX

wifi: mt76: mt792x: skip MLD header rewrite for 802.3 encap TX

mt792x_tx() rewrites addr1/addr2/addr3 by treating skb->data as
an 802.11 header for MLD traffic.

That is only valid for native 802.11 frames. Direct 802.3 TX can also
reach this path with IEEE80211_TX_CTL_HW_80211_ENCAP set, where
skb->data is not an 802.11 header.

Skip the MLD header rewrite for HW-encap packets to avoid corrupting
802.3 frame contents.

Fixes: ebb1406813c6 ("wifi: mt76: mt7925: add link handling to txwi")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260425144648.734030-1-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>