i40e: ignore duplicate port VLAN requests

If user attempts to set a port VLAN on a VF that already has the same
port VLAN configured, the driver will go through a completely
unnecessary flurry of filter removals and filter adds. Just check for
this condition and return success instead of doing a bunch of busywork.

Change-ID: Ia1a9e83e6ed48b3f4658bc20dfc6af0cf525d54a
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>