net/mlx5_core: Initialize namespaces only when supported by device

Before we create the sub tree of a steering namespaces(kernel, bypass,
leftovers) we check that the device has the required capabilities
in order to create this subtree.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>