net/mlx5: E-Switch, Enable setting goto slow path chain action

A pre-step for the tc offloads code to use this when a neigh is
not available for encap rules.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>