net/mlx5e: Add TX stateless offloads for tunneling

Add support for TSO and TX checksum when using hw assisted,
tunneled offloads.

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