ixgbe: add support for VF Transmit rate limit using iproute2

Implemented ixgbe_ndo_set_vf_bw function which is being used by iproute2
tool. In addition, updated ixgbe_ndo_get_vf_config function to show the
actual rate limit to the user.

The rate limitation can be configured only when the link is up and the
link speed is 10Gb.
The rate limit value can be 0 or ranged between 11 and actual link
speed measured in Mbps. A value of '0' disables the rate limit for
this specific VF.

iproute2 usage will be 'ip link set ethX vf Y rate Z'.
After the command is made, the rate will be changed instantly.
To view the current rate limit, use 'ip link show ethX'.

The rates will be zeroed only upon driver reload or a link speed change.

This feature is being supported by 82599 and X540 devices.

Signed-off-by: Lior Levy <lior.levy@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>