net/mlx5e: don't assume psp tx skbs are ipv6 csum handling

net/mlx5e: don't assume psp tx skbs are ipv6 csum handling

mlx5e_psp_handle_tx_skb() assumes skbs are ipv6 when doing a partial
TCP checksum with tso. Make correctly mlx5e_psp_handle_tx_skb() handle
ipv4 packets.

Fixes: e5a1861a298e ("net/mlx5e: Implement PSP Tx data path")
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Link: https://patch.msgid.link/20260126-dzahka-fix-tx-csum-partial-v2-1-0a905590ea5f@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>