net/mlx5e: Fix checksum handling for non-stripped vlan packets

Now as rx-vlan offload can be disabled, packets can be received
with vlan tag not stripped, which means is_first_ethertype_ip will
return false, for that we need to check if the hardware reported
csum OK so we will report CHECKSUM_UNNECESSARY for those packets.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>