ixgbe: add a callback to set the maximum transmit bitrate

This commit adds a callback which allows to adjust the maximum transmit
bitrate the card can output. This makes it possible to get a smooth
traffic instead of the default burst-y behaviour when trying to output
e.g. a video stream.

Much of the logic needed to get a correct bcnrc_val was taken from the
ixgbe_set_vf_rate_limit() function.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c
index 4bc24963..adcf000 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_sriov.c
@@ -1398,7 +1398,7 @@
 	return err;
 }
 
-static int ixgbe_link_mbps(struct ixgbe_adapter *adapter)
+int ixgbe_link_mbps(struct ixgbe_adapter *adapter)
 {
 	switch (adapter->link_speed) {
 	case IXGBE_LINK_SPEED_100_FULL: