ixgbe: Save VF info and take references

Save VF device pointers and take references to speed accesses used
to monitor the device behavior to avoid slot resets. The saved
information avoids lock contention during the search used to access
each of the VFs.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>