ixgbevf: Use cached link state instead of re-reading the value for ethtool

Change the ethtool link settings call to just read the cached state out of
the adapter structure instead of trying to recheck the value from the PF.
Doing this should prevent excessive reading of the mailbox.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: "Guilherme G. Piccoli" <gpiccoli@canonical.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>