RDMA/mlx5: Block delay drop to unprivileged users

RDMA/mlx5: Block delay drop to unprivileged users

commit 4f3378e7fa3a1af0475dd3a165f7fb49d591ad69 upstream.

It has been discovered that this feature can globally block the RX port,
so it should be allowed for highly privileged users only.

Fixes: d595d951527f("IB/mlx5: Add support to dropless RQ")
Link: https://lore.kernel.org/r/20200322124906.1173790-1-leon@kernel.org
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>