net/mlx5: DR, Add the internal direct rule types definitions

Add the internal header file that contains various types
definition that will be used in coming patches as well as
the internal functions decelerations.

Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Yevgeny Kliteynik <kliteyn@mellanox.com>
Reviewed-by: Erez Shitrit <erezsh@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>