net/mlx5: add ID generation

net/mlx5: add ID generation

When splitting flows for example in hairpin / metering, there is a need
to combine the flows. This is done using ID.
This commit introduce a simple way to generate such IDs.

The reason why bitmap was not used is due to fact that the release and
allocation are O(n) while in the chosen approch the allocation and
release are O(1)

Signed-off-by: Ori Kam <orika@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>