net/mlx4_en: Enable TX rate limit per VF

Support granular QoS per VF, by implementing the ndo_set_vf_rate.

Enforce a rate limit per VF when called, and enabled only for VFs in
VST mode with user priority supported by the device.

We don't enforce VFs to be in VST mode at the moment of configuration,
but rather save the given rate limit and enforce it when the VF is
moved to VST with user priority which is supported (currently 0).

VST<->VGT or VST qos value state changes are disallowed when a rate
limit is configured. Minimum BW share is not supported yet.

Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>