ixgbe: set driver_max_VFs should be done before enabling SRIOV

commit 43dc4e01 Limit number of reported VFs to device
 specific value It doesn't work and always returns -EBUSY because VFs are
 already enabled.

ixgbe_enable_sriov()
        pci_enable_sriov()
                sriov_enable()
                {
                ... ..
                iov->ctrl |= PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE;
                pci_cfg_access_lock(dev);
                ... ...
                }

pci_sriov_set_totalvfs()
{
... ...
if (dev->sriov->ctrl & PCI_SRIOV_CTRL_VFE)
                return -EBUSY;
...
}

So should set driver_max_VFs with pci_sriov_set_totalvfs() before
enable VFs with ixgbe_enable_sriov().

V2: revised for net-next tree.

Signed-off-by: Ethan Zhao <ethan.kernel@gmail.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>