fm10k: add support for ndo_get_vf_stats operation

Support capturing and reporting statistics for all of the VFs associated
with a given PF device via the ndo_get_vf_stats callback.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>