net/mlx5e: Support offloaded TC flows with no matches on headers

For example:
    tc filter add dev ens2f0_0 parent ffff: flower skip_sw action drop

Note that for eswitch flows, we still always match on the source port.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>