net/mlx5: Add user chosen levels when allocating flow tables

Currently, consumers of the flow steering infrastructure can't
choose their own flow table levels and are limited to one
flow table per level. This just waste levels.
Instead, we introduce here the possibility to use multiple
flow tables in a level. The user is free to connect these
flow tables, while following the rule (FTEs in FT of level x
could only point to FTs of level y where y > x).

In addition this patch switch the order of the create/destroy
flow tables of the NIC(vlan and main).

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>