igb: remove sysfs entry that was used to set the number of vfs

This patch removes the sysfs entry num_vfs which was added to support
enabling pci virtual functions for 82576.

To prevent VFs from loading automatically a module parameter "max_vfs" was
added so that the number of VFs per PF can be limited.  This is especially
useful when 4 or more 82576 ports are on the system because otherwise to
load all VFs would result in 8 interface per physical port.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>