net/mlx5e: Fix driver's declaration to support GRE offload

Declare GRE offload support with respect to the inner protocol. Add a
list of supported inner protocols on which the driver can offload
checksum and GSO. For other protocols, inform the stack to do the needed
operations. There is no noticeable impact on GRE performance.

Fixes: 27299841 ("net/mlx5e: Support TSO and TX checksum offloads for GRE tunnels")
Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>