net/mlx5: DR, Improve rule tracking memory consumption

To track each STE of the rule a rule member was allocated, each
member would point to one STE. This means that we would allocate
40B (rule member) * number of STEs per rule.

To reduce this per rule allocation we use the STE tree pointers
for next_htbl and pointing STE to navigate the tree, this allows
us to keep only the pointer to the last STE of rule (always unique).
From the last rule STE we are able to traverse and rebuild all of
the STEs that construct the rule.

In our testing with 8M rules, each consisting of 7 STES, we were able
to reduce 1.6GB of memory.

Signed-off-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Erez Shitrit <erezsh@nvidia.com>
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>