net/mlx5e: Add VLAN offload features to hw_enc_features

We support outer VLAN offload in driver and HW regardless of whether
an encapsulation is present in the next headers.

Exposing this in hw_enc_features will allow us to offload outer VLANs
in cases where encapsulation protocols like VXLAN and IPsec are used.

Signed-off-by: Aviv Heller <avivh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>