Backport Mellanox mlx5 patches to stable 4.9.y

[Marta Rybczynska]

Hello Mellanox maintainers,
I'd like to ask you to OK backporting two patches in mlx5 driver to 4.9 stable
tree (they're in master for some time already).

We have multiple deployment in 4.9 that are running into the bug fixed by those
patches. We're deploying patched kernels and the issue disappears.

The patches are:
1410a90ae449061b7e1ae19d275148f36948801b net/mlx5: Define interface bits for fencing UMR wqe
6e8484c5cf07c7ee632587e98c1a12d319dacb7c RDMA/mlx5: set UMR wqe fence according to HCA cap
 
Regards,
Marta