net/mlx: control netdevices through ioctl only

net/mlx: control netdevices through ioctl only

Several control operations implemented by these PMDs affect netdevices
through sysfs, itself subject to file system permission checks enforced by
the kernel, which limits their use for most purposes to applications
running with root privileges.

Since performing the same operations through ioctl() requires fewer
capabilities (only CAP_NET_ADMIN) and given the remaining operations are
already implemented this way, this patch standardizes on ioctl() and gets
rid of redundant code.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>