net/mlx5: Add flow steering actions to fs_cmd shim layer

Add flow steering actions: modify header and packet reformat
to the fs_cmd shim layer. This allows each namespace to define
possibly different functionality for alloc/dealloc action commands.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>