net/mlx5e: Set default can_offload action

Many parsers of tc actions just return true on their can_offload()
implementation, without checking the input flow/action.
Set the default can_offload action to true (allow), and avoid
having many can_offload implementations that do just that.

This patch doesn't change any functionality.

Signed-off-by: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>