ixgbevf: add netpoll support

This patch adds ixgbevf_netpoll() a callback for .ndo_poll_controller to
allow for the VF interface to be used with netconsole.

CC: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>