net/mlx5: Use underlay QPN from the root name space

Root flow table is dynamically changed by the underlying flow steering
layer, and IPoIB/ULPs have no idea what will be the root flow table in
the future, hence we need a dynamic infrastructure to move Underlay QPs
with the root flow table.

Fixes: b3ba5149

 ("net/mlx5: Refactor create flow table method to accept underlay QP")
Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>