net: ethernet: mediatek: Add metadata support for xdp mode

Set metadata size building the skb from xdp_buff in mediatek driver.
mtk_eth_soc driver sets xdp headroom to XDP_PACKET_HEADROOM so the
headroom is large enough to contain xdp_frame and xdp metadata.
Please note this patch is just compiled tested.

Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250318-mvneta-xdp-meta-v2-5-b6075778f61f@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>